AMMAN // Middle East powers that oppose the Syrian president, Bashar Al Assad, have dramatically stepped up supplies of weapons to the rebels battling his forces in preparation for a push on Damascus, according to officials and military experts.
Jordan, Saudi Arabia, Turkey and Qatar are involved in a carefully prepared operation to arm the opposition forces, with the United States and other western governments consulting, according to a senior Arab official whose government is participating. His account was corroborated by a diplomat and two military experts.
All parties hold power of veto over where the shipments are sent, the official added.
He said the number of arms airlifts had doubled in the past four weeks but did not provide exact figures for the flights or the size of the cargo.
Jordan opened up as a new route for the weapons late last year, amid US fears that arms from Turkey were going to Islamists, all four sources said.
Jordan has denied helping to funnel weapons to the rebels.
The military experts, who closely follow the traffic, said the weapons included Croatian-made anti-tank guns and rockets, which are more powerful than those rebels have been using until now.
The Arab official said that there was a "master plan" in place for the rebels to seize Damascus.
"The idea is that the rebels now have the necessary means to advance from different fronts - north from Turkey, and south from Jordan - to close in on Damascus to unseat Assad," the he said.
Rebels have captured suburbs around Damascus but have been largely unable to break into the capital. Instead, they have hit central neighbourhoods of the city with increasingly heavy mortar volleys from their positions to the north-east and south.
But opposition forces in the south are fighting to secure supply lines from the border with Jordan to the capital, and the influx of weapons from Jordan has fuelled the drive, a rebel commander in a southwestern suburb of the capital said.
Syria's rebels, who are divided into numerous independent brigades, have long complained that the international community was not providing them with the weaponry needed to defeat Mr Al Assad.
But the US in particular has been wary of arming the rebellion, fearing weapons will go to Islamists, who have taken a prominent role in the uprising.
The sources said the material was destined for "secular" fighters not necessarily linked to the Free Syrian Army, the nominal umbrella group for the rebels.
Jordan and other Arabs have been critical of the FSA, which they accuse of having failed as an effective or credible force.
The sources described a system in which Saudi Arabia and Qatar provided the funding for the weapons, while Jordan and Turkey provided the land channels for the shipments to reach the rebels.
The Jordanian information minister, Sameeh Maayatah, insisted the kingdom was not helping funnel weapons. "Jordan is neither assisting the Assad regime, nor its opponents," he said. Instead, he argued, Jordan wanted a "quick political solution" to the Syrian crisis.
The Turkish Foreign Ministry would not confirm weapons transfer through Turkey, saying: "We have no official information to confirm such reports or claims."
The US secretary of state, John Kerry, said last month that the weapons were ending up in the hands of secular groups.
Wrapping up a summit in Qatar on Tuesday, Arab states underlined their right to arm the Syrian rebels, noting the growing frustration with Mr Al Assad's regime and with what was believed to be a supply of weapons flowing to his regime from his main ally, Iran.
The opening of a weapons pipeline through Jordan "provides a fresh approach" to Syrian rebels, said Shashank Joshi, a military expert who has been monitoring the arms flow for two years for the Royal United Services Institute, a British think tank.
Hugh Griffiths, a Sweden-based arms-trafficking expert with the Stockholm International Peace Research Institute, said about 3,500 tonnes of military equipment had been shipped to rebels since traffic began early last year. He said there had been at least 160 airlifts from Saudi Arabia, Qatar and, later, Jordan, with the most recent being a shipment of unspecified items from Qatar to Turkey on Sunday.
Two prominent independent researchers monitoring weapons traffic - Eliot Higgins in Britain and Nic Jenzen-Jones in Australia - said Croatian arms began appearing only recently in Syria.
They included M60 recoilless guns, M79 Osa rocket launchers, and RBG-6 grenade launchers, all of which are powerful anti-tank weapons.
Mr Griffiths said the Croatian arms were a "major game changer" as they are "portable, but pack a much bigger explosive punch".