US Senator John McCain crossed from Turkey into Syria Monday to meet with rebel leaders in the war-torn nation, according to a spokesman for the top lawmaker who advocates arming the Syrian opposition.
McCain, the 2008 Republican presidential nominee, slipped across the border in an unannounced visit lasting several hours before he returned to Turkey.
"I can confirm the trip. It was today," aide Brian Rogers said, confirming a report that first appeared on The Daily Beast, adding that no other lawmakers traveled with McCain into Syria.
The visit came as US Secretary of State John Kerry met his Russian counterpart in Paris for talks aimed at breathing life into a peace conference on ending the conflict in Syria, where tens of thousands of people have been killed since March 2011.
The Daily Beast, a US news website, said that McCain entered the country with General Salem Idris, leader of the Supreme Military Council of the Free Syrian Army.
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During the talks, rebel leaders asked for increased US support to the Syrian opposition by providing heavy weapons, establishing a no-fly zone and carrying out air strikes on Syrian regime forces, The Daily Beast reported.
"The visit of Senator McCain to Syria is very important and very useful especially at this time," the report quoted Idris as saying.
"We need American help to have change on the ground; we are now in a very critical situation."
McCain is among the sharpest critics of the Syria policy of US President Barack Obama, who has signed off on Washington providing non-lethal and humanitarian aid to the rebels but has so far refused to provide arms.
Syrian President Bashar al-Assad's forces have mounted intense assaults on the rebels over the past week, particularly in the insurgent bastion of Qusayr, in central Syria.
Earlier this month, US ambassador to Syria Robert Ford -- who was recalled from Damascus in October 2011 over concerns for his safety -- met with a Syrian rebel chief at a border crossing with Turkey.