US Secretary of State John Kerry insisted Thursday Syrian President Bashar al-Assad will have to step down as part of any political solution in Syria, as he held a third day of talks on the bloody conflict.
Kerry on Tuesday seemed to soften the US stand on Assad's future as a concession to Russia's concern.
Meanwhile, the United Nations on Wednesday pulled peacekeepers back from an observation post in the Golan Heights ceasefire zone where four Philippine troops were abducted by Syrian rebels, a spokesman said.
The move came as countries which contribute troops to the UN Disengagement Observer Force (UNDOF) expressed renewed concern about security in the zone between Israel and war-stricken Syria.
Speaking as he met Jordanian Foreign Minister Nasser Judeh, Kerry said all sides were working to "effect a transition government by mutual consent of both sides, which clearly means that in our judgement President Assad will not be a component of that transitional government."
Kerry also officially unveiled $100 million in additional US humanitarian aid for Syrian refugees, almost half of which will go to help Jordan struggling to cope with a tide of people fleeing the 26-month war.
Plans for an international conference to try to find a solution to the crisis were also continuing, Kerry said, after he agreed Tuesday in Moscow talks that he and Russian Foreign Minister Sergei Lavrov would work in tandem on the issue.
It is hoped the conference could be held by the end of May. Although no venue has yet been identified, the Swiss city could again host the talks.
Syria, meanwhile, restored Internet services on Wednesday afternoon after a two-day blackout, residents and state media said.
State media blamed the blackout on a technical fault but activists and a watchdog accused the regime of deliberating cutting the connection to shield military operations.