The former chief of the main opposition Syrian National Council, Burhan Ghalioun, told AFP he visited Syria for a few hours on Tuesday to "boost the morale" of rebels.
Ghalioun, a senior SNC executive board member, spoke to AFP in Beirut by telephone after his first visit to Syria in more than two years, and said he entered the country secretly and had "discussions with revolutionaries."
"The visit was aimed at boosting the morale of rebels," who are fighting the regime of Syrian President Bashar al-Assad, Ghalioun said after returning to neighbouring Turkey.
"The visit was also a bit to offer compassion to our people who have been killed, massacred and slaughtered" by regime forces, he added.
The former SNC chief said he visited "several regions in Idlib province" a rebel stronghold in northwest Syria near the border with Turkey.
"Of course there was some danger involved, because the shelling doesn't stop but we took precautionary measures to avoid these dangers as much as possible," he said.
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"The regime is very weak and has lost control on the ground," he added.
"Today Syria is being rebuilt by its own citizens," he said.
A video posted by activists on the Internet shows Ghalioun wearing a flowing abaya robe, a chequered keffiyeh on his head, kneeling and kissing the ground.
A second video shows the opposition leader surrounded by a group of youths in military garb and carrying machine guns. "We came to see you," one of them is heard saying as another offers Ghalioun a cup of coffee.
In a third video one of the young fighters is heard telling Ghalioun "we are running out of time" prompting the opposition leader to take leave of the group and get into a waiting car for his trip out of Syria.
But before leaving Ghalioun flashes the V for victory sign as the fighters bid him farewell with shouts of: "May God protect you."
Ghalioun resigned in May to avert divisions within the opposition bloc, after activists on the ground accused him of monopolising power. But he remains one of the main opposition leaders and a member of the executive board of the SNC.
Earlier this month, the SNC named Kurdish activist Abdel Basset Sayda to replace Ghalioun in a bid to gain broader appeal that could embrace all groups.