McCain met with 18 commanders of the rebel Free Syrian Army near the country's northern border.
He says Mr Wahbh was held for 53 days by the rebel Free Syrian Army.
The Free Syrian Army opposition fighters have been attacking the Shabiha and getting their weapons.
The rebels of the Free Syrian Army have already declared the Annan mission dead.
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The rebel Free Syrian Army is thought to receive weapons and other supplies from Turkey.
The Free Syrian Army has threatened to attack Hezbollah in Lebanon if it doesn't leave Syria.
It credited the Free Syrian Army with shooting down a government warplane in Adra.
There were also some skirmishes between security forces and rebel fighters from the Free Syrian Army.
The majority fighting on the opposition side are defectors calling themselves the Free Syrian Army.
Chants include, "The Free Syrian Army forever, we'll trample on the head of Assad".
Loyalist forces wield far greater firepower than the ragtag rebel bands of the Free Syrian Army.
Louay Almokdad, a spokesman for the rebel Free Syrian Army, said he was shocked by the report.
They included 45 in Damascus and its suburbs, many of them members of the Free Syrian Army.
It follows clashes between the Free Syrian Army and the security forces in the area on Wednesday.
He said the dead include at least 300 civilians and 150 members of the rebel Free Syrian Army.
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"I myself went to two exchange negotiations, " said Louai Miqdad, a spokesman for the rebel Free Syrian Army.
Fighting has intensified as groups such as the Free Syrian Army pose a challenge for government security forces.
Frequent clashes between the army and Free Syrian Army in central districts have already shattered any illusion of peace.
The Free Syrian Army said it fired rockets from Qusayr across the border into northeastern Lebanon, targeting Hezbollah areas.
The Free Syrian Army (FSA) - the main rebel fighting force - condemned the seizure of the UN observers.
But he said that, while the Free Syrian Army has a presence in Damascus, it remains outmanned and outgunned.
The Military Council nominally falls under the main rebel umbrella Free Syrian Army.
Abdullah Odah of the Free Syrian Army, the armed Syrian opposition, in Istanbul.
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Nearly two years into the uprising, the rebel Free Syrian Army continues to be dogged by accusations of corruption.
Some groups like Tawhid claim to work under the Free Syrian Army, whose secular figureheads are based in Turkey.
But he's accepted by the mostly Sunni members of the Free Syrian Army.
For the third day, Free Syrian Army fighters tried to wrest control of the helicopter base from government forces.
And rocket fire, apparently from the Free Syrian Army, has landed in Shiite areas around the Lebanese town of Hermel.
Clashes between Free Syrian Army rebels and regime forces were taking place near the city's Central Prison, the LCC said.
But a spokesman for the rebel Free Syrian Army told CNN he believes the attack was staged by the government.
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