Amid reports that the Syrian military is secretly stockpiling chemical weapons, U.N. human rights investigators allegedly have testimony indicating Syrian rebels have used sarin gas. Interviews with victims and doctors have provided “strong, concrete suspicions” that rebels used the deadly nerve agent, according to a lead investigator, though the U.N. does not have “incontrovertible proof.” There’s no evidence yet that the Syrian military used sarin. The latest Geneva-based investigation is separate from U.N. Secretary-General Ban Ki-moon’s currently stalled inquiry into the use of chemical weapons in Syria.

Reuters:

U.N. human rights investigators have gathered testimony from casualties of Syria's civil war and medical staff indicating that rebel forces have used the nerve agent sarin, one of the lead investigators said on Sunday.

The United Nations independent commission of inquiry on Syria has not yet seen evidence of government forces having used chemical weapons, which are banned under international law, said commission member Carla Del Ponte.

"Our investigators have been in neighboring countries interviewing victims, doctors and field hospitals and, according to their report of last week which I have seen, there are strong, concrete suspicions but not yet incontrovertible proof of the use of sarin gas, from the way the victims were treated," Del Ponte said in an interview with Swiss-Italian television.

"This was use on the part of the opposition, the rebels, not by the government authorities," she added, speaking in Italian.

Del Ponte, a former Swiss attorney-general who also served as prosecutor of the International Criminal Tribunal for the former Yugoslavia, gave no details as to when or where sarin may have been used.

Israeli warplanes have targeted Syria twice in the last three days, and now Israel is deploying two batteries of its Iron Dome rocket defense system to the north of the country. The second airstrike early Sunday, hit a military facility just north of the capital, a Western intelligence expert confirmed. Israel declined to comment. “The sky was red all night,” said one man who lives less than a mile from the facility. “We didn’t sleep a single second. The explosions started after midnight and continued throughout the night.” The facility reportedly held Iranian-supplied missiles, which Israel contends were headed for Lebanon’s Hezbollah. Israel attacked the same site three months ago. President Obama, meanwhile, defended Israel on Sunday.

A suicide bombing tore through a mosque in the Syrian capital Thursday, killing a top Sunni Muslim preacher and longtime supporter of President Bashar Assad along with at least 41 other people.

Syrian extremists have killed the wrong Sunni cleric. Sheikh Mohammad Said Ramadan al-Buti, a top Sunni preacher and supporter of President Bashar al-Assad, was one of 42 people killed in a suicide bombing at a mosque in Damascus on Friday. In response, Assad has stated that his forces will “wipe out” and “clean our country” of the Muslim extremists he believes are responsible for the attack, the first to target a mosque since the country’s civil war began two years ago. Meanwhile, the United Nations plans to investigate whether either the Syrian government or its rebel opposition has used chemical weapons against one another, as they both have claimed.

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It was one of the most stunning assassinations of the two-year civil war and marked a new low in the conflict: while suicide bombings blamed on Islamic extremists fighting with the rebels have become common, the latest attack was the first time a suicide bomber detonated his explosives inside a mosque. The grandson of the 84-year-old al-Buti was among those killed in the attack.

In the statement carried by Syria's state SUNA news agency, Assad said al-Buti represented true Islam in facing "the forces of darkness and extremist" ideology.

"Your blood and your grandson's, as well as that of all the nation's martyrs will not go in vain because we will continue to follow your thinking to wipe out their darkness and clear our country of them," said Assad.

Syria's crisis started in March 2011 as peaceful protests against Assad's authoritarian rule. The revolt turned into a civil war as some opposition supporters took up arms the fight a harsh government crackdown on dissent. The U.N. says more than 70,000 people have been killed since.

It is not yet clear when al-Buti's funeral would take place, although the Syrian government declared Saturday as a day of mourning.

In what would be a deadly new low in the Syrian conflict, both sides are accusing each other of launching a chemical attack near the city of Aleppo. A Reuters photographer visited a hospital where people were suffering from breathing problems. “I saw mostly women and children,” he said. “They said that people were suffocating in the streets and the air smelt strongly of chlorine.” The Syrian government claims the rebels launched a chemical-laden rocket, killing at least 25 people and wounding 86, while the rebels say the regime fired the weapon. President Obama previously warned Syrian President Bashar al-Assad that the use of chemical weapons would be a “red line.”

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Information Minister Omran al-Zoabi said rebels fired "a rocket containing poison gases" at the town of Khan al-Assal, southwest of Aleppo, from the city's southeastern district of Nairab, part of which is rebel-held.

"The substance in the rocket causes unconsciousness, then convulsions, then death," the minister said.

But a senior rebel commander, Qassim Saadeddine, who is also a spokesman for the Higher Military Council in Aleppo, denied this, blaming Assad's forces for the alleged chemical strike.

"We were hearing reports from early this morning about a regime attack on Khan al-Assal, and we believe they fired a Scud with chemical agents," he told Reuters by telephone from Aleppo.

Republican Senator Lindsey Graham (R-SC) on Tuesday was already calling for the U.S. to put American troops on the ground inside Syria to secure the weapons of mass destruction.

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Graham told The Cable in an interview Tuesday that whether or not the attack can be confirmed as the first use of chemical weapons in the 24-month Syrian civil war, the United States must devise and implement a plan to secure Syrian chemical weapons sites and deploy U.S. troops to do it if necessary.

"My biggest fear beyond an Iranian nuclear weapons capability is the chemical weapons in Syria falling in the hands of extremists and Americans need to lead on this issue. We need to come up with a plan to secure these weapons sites, either in conjunction with our partners if nothing else by ourselves," Graham said.

Asked if he would support sending U.S. troops inside Syria for the mission, Graham said yes.

"Absolutely, you've got to get on the ground. There is no substitute for securing these weapons," he said. "I don't care what it takes. We need partners in the region. But I'm here to say, if the choice is to send in troops to secure the weapons sites versus allowing chemical weapons to get in the hands of some of the most violent people in the world, I vote to cut this off before it becomes a problem."

Watch The Battle for Syria on PBS. See more from FRONTLINE.

Frontline journeys to the heart of the Syrian insurgency, embedding with rebels who are waging a full-scale assault on Assad’s forces. But how organized are Syria’s opposition groups? What dangers might the conflict unleash? And what would it take to end it?

Frontline turned to 10 experts — Syrian activists, journalists who have reported from the country’s dangerous front lines and analysts who specialize in the region — to explain the long-term impacts of Syria’s deadly conflict.

The video above shows the areas of Syria that are experiencing violent clashes and shelling on Tuesday morning.

The Syrian regime is using Twitter to try to clarify recent comments about the country's weapons of mass destruction.

Syrian officials said Monday that they would use chemical and biological weapons if foreign countries intervene in the escalating civil war. Foreign ministry spokesman Jihad Makdissi said the army would not use the weapons against the rebels, but rather if “Syria faces external aggression.” Syria did not a sign a 1992 international convention that banned the stockpiling of chemical weapons, although its leaders have long denied having weapons stockpiles. Although Damascus residents did not report new fighting in the capital early Tuesday, residents in Aleppo reported shelling and clashing.
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However, on Tuesday morning, Makdissi seems to be walking back his statement a bit:

"The Foreign Ministry's statement was only a response to false allegations on WMD & explanation of guidelines of defensive policy," ministry spokesman Jihad Makdissi tweeted on Tuesday.

You've got people talking about forcibly removing you from your country, and you take to "Twitter" to clarify your remarks on weapons of mass destruction?