United Nations chemical weapons inspectors are back in Syria to investigate the use of the banned arms in the country's two-and-a-half-year civil war.
The team led by Ake Sellstrom flew into neighboring Lebanon on Wednesday and traveled by car to Damascus.
They first went to Syria last month to investigate three attacks, including one in March outside of Aleppo that the Syrian government and rebel fighters blamed on each other.
The team shifted their focus on the two-week mission to a fresh attack outside Damascus, where they concluded chemical weapons had been used. The team's mandate does not include assigning blame for any chemical attacks.
Also Wednesday, a group of 13 rebel groups issued a joint statement rejecting the main opposition Syrian National Council, saying it no longer represented their interests. The group, which includes the al-Qaida-linked Nusra Front called on those fighting against President Bashar al-Assad to unite under an Islamic framework.
Meanwhile, diplomats are continuing to work on a draft resolution to enforce an agreement for Syria to give up its chemical weapons.
U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov met Tuesday on the sidelines of the U.N. General Assembly in New York, but failed to agree on the key points of the document.
U.S. officials say points of contention remain as the two sides seek a deal on the language of the resolution. The U.S. and Russian ambassadors to the U.N. are tasked with working out the final language.
Russia opposes a resolution that mentions Chapter VII of the U.N. charter, which includes military and non-military action to enforce decisions.
Russia has long opposed the idea of military intervention, and has vetoed three attempts to sanction Syria at the U.N. Security Council.
Russian Deputy Foreign Minister Sergei Ryabkov said Tuesday the resolution could mention the Chapter VII article that permits force or sanctions, only if the U.S.-Russia chemical weapons accord is violated by either side in the Syrian conflict.
Speaking at the General Assembly Tuesday, U.S. President Barack Obama criticized doubters who questioned whether Syrian President Bashar al-Assad carried out a chemical attack last month near Damascus. U.S. intelligence says the attack killed 1,400 people.
Syria's civil war has forced 2 million people to flee the country, with another 4.5 million displaced within Syria. In total, the conflict has forced more than a quarter of Syria's population to leave their homes.
Most of those who have fled the country have gone to neighboring countries, including Jordan, Lebanon, Turkey and Iraq.