The goal is still to bring the Assad regime and representatives from the opposition together for talks on setting up an interim government, Kerry said. The Geneva plan, which never gained traction, allowed each side to veto candidates it found unacceptable.
In Syria, meanwhile, rebels detained four U.N. peacekeepers on Tuesday near the frontier with the Israeli-controlled Golan Heights, raising tensions just two days after the most recent Israeli airstrike.
The abduction was the second such incident in the area in two months. It exposed the vulnerability of the U.N. peacekeeping mission during the Syrian civil war and sent a worrisome signal to Syria's neighbors - including Israel - about the ensuing lawlessness along their shared frontiers.
Rebels with the Yarmouk Martyrs Brigades are holding the peacekeepers, a spokesman said in a phone interview. The Yarmouk Brigades were behind the abduction in March of 21 Filipino U.N. peacekeepers released unharmed after four days of negotiations. The spokesman spoke on condition of anonymity because he was outside of Syria serving as a mediator on peaceful matters concerning the group.
In New York, Kieran Dwyer, spokesman for the U.N. peacekeeping department, confirmed the abduction and said the four peacekeepers, all from the Philippines, were taken on Tuesday by an unidentified armed group near the town of Jamla in southern Syria.
"Efforts are underway to secure their release now," Dwyer said.
In a statement posted on the Yarmouk Brigades' Facebook page, the group said the peacekeepers were not hostages, but were being held for their own safety. The statement did not specify where the peacekeepers were being held, nor did it specify conditions for their release.
The rebel unit said it suspects the U.N. peacekeepers are shielding Assad's troops, who the rebels said killed civilians during an army sweep of Wadi Raqat in the south.
The U.N. monitoring mission was set up in 1974, seven years after Israel captured the Golan Heights and a year after it managed to push back Syrian troops trying to recapture its territory in another regional war. For nearly four decades, the U.N. monitors have helped enforce a stable truce between Israel and Syria. But in recent months, Syrian mortar shells overshooting their target have repeatedly hit the Israeli-controlled Golan.