Rebels in southern Syria say they are planning a spring offensive against Damascus, which regime and opposition sources say will include fighters trained by Western forces in neighbouring Jordan.
The Syrian army, meanwhile, is redeploying troops in Quneitra province located on the ceasefire line with Israel, and stepping up shelling on rebel positions in Daraa on the Jordan border to stop any advance, opposition fighters say.
The looming showdowns come after regime and opposition representatives failed last week to reach consensus at talks in Geneva, and amid reports that some Gulf Arab states have pledged to arm the rebels.
Both regime and opposition sources say the offensive on Damascus will involve thousands of rebels who have been receiving combat training for the past year from the United States and other Western countries in Jordan.
"Daraa (province) is the gateway to Damascus. The battle for Damascus starts from here," said rebel commander Abdullah al-Qarazi, an ex-officer in the Syrian army.
"For now, we only have guarantees (for weapons) from the countries that support" the revolt against President Bashar al-Assad, he said.
"If the promises are honoured, God willing we will reach the heart of the capital," in a bid to break army sieges on the Western and Eastern Ghouta districts outside the capital, Qarazi told AFP.
Qarazi, a brigadier general in the Syrian army before defecting, said rebels in Daraa have "made steady progress in recent months" despite intensifying army bombardment of the province.
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Since last summer, rebels have seized parts of Daraa city and several positions close to the border with Jordan, which could be used as a conduit for arms.
Rebels also set up a coalition of 47 factions and opened communications channels with fighters in Damascus province and in Quneitra, the main town in the Syrian Golan Heights parts of which have been annexed by Israel.
But the army is preparing to fight back, "redeploying troops" to the Quneitra front from areas of Damascus, said Ali al-Jolani of Quneitra's rebel military council.
And a Syrian politician told AFP that a major battle is planned in Daraa ahead of a possible fresh round of peace talks between the regime and the opposition.
The second round broke down on the weekend with no progress achieved and no date was announced by the UN-Arab League envoy Lakhdar Brahimi.
A source close to the regime has said the talks could resume next month but this could not be independently verified.
Meanwhile the Syrian army has in recent days stepped up air raids on the southern province and pounded rebel areas and villages with explosive-packed barrels, a monitoring group said.
On Tuesday, the air force launched three barrel bomb attacks, one of which killed 13 people including three children, said the Syrian Observatory for Human Rights.
Last week the Wall Street Journal reported that Gulf backers of the anti-Assad revolt were preparing to deliver weapons to the rebels, including "both shoulder-fired missiles capable of taking down military aircraft and anti-tank missiles."