UNITED NATIONS // Iran has significantly stepped up military support to the Syrian president, Bashar Al Assad, in recent months, solidifying its position alongside Russia as the government's lifeline in an increasingly sectarian civil war, western diplomats say.
Iranian weapons continue to pour into Syria from Iraq but also increasingly along other routes, including via Turkey and Lebanon, in violation of a UN arms embargo on Iran, western officials said. Iraqi and Turkish officials denied the allegations.
Iran's acceleration of support for Mr Al Assad suggests the Syrian war is entering a new phase in which Iran may be trying to end the battlefield stalemate by redoubling its commitment to the regime.
It also highlights the growing sectarian nature of the conflict, with Iranian arms flowing to the Shiite militant group Hizbollah. That group is increasingly active on the ground in Syria in support of Mr Al Assad's forces, envoys say.
The Syrian conflict started out two years ago as a pro-democracy movement. About 70,000 people have been killed and more than 1 million refugees have fled the violence.
A western intelligence report in September said Iran was using civilian aircraft to fly military personnel and large quantities of weapons across Iraqi airspace to aid Mr Al Assad. Iraq denied that report.
Much of the weaponry going to Syria now, diplomats say, continues to be shipped from Iran through Iraqi airspace and overland through Iraq, despite Baghdad's repeated promises to put a stop to Iranian arms supplies.
"The Iranians really are supporting massively the regime," a western diplomat said this week. "They have been increasing their support for the last three, four months through Iraq's airspace and now lorries. And the Iraqis really are looking the other way."
Hizbollah was "hardly hiding the support it's giving to the (Syrian) regime", the diplomat added.
He added that the Syrian civil war was becoming "more and more sectarian", with Sunnis - an increasing number of whom come from Iraq - battling Shiites and members of Mr Al Assad's Alawite sect, an offshoot of Shiite Islam.
Ali Al Moussawi, the media adviser to the Iraqi prime minister, Nouri Al Maliki, denied the allegations, saying: "No, such a thing never happened. Weapons did not and will not be transferred from Iran to Syria through Iraq, whether by land or by air."
Russia, diplomats said, also remained a key arms supplier for Assad. Unlike Iran, neither Syria nor Russia is subject to a UN ban on arms trade.
Russia, an ally of Assad's regime, criticises US, European and Gulf Arab governments for their aid to Syrian rebels.
Russia has said repeatedly that its military support for Syria includes anti-missile air defence systems but no attack weapons, such as helicopters.
Moscow says it is not wedded to Mr Al Assad but that the rebels and government should talk and the president's departure should not be a condition for a deal as the opposition and its supporters insist. Along with China, it has used its Security Council veto to block punitive UN measures against Syria's government.
Alireza Miryousefi, spokesman for Iran's UN mission, said: "We believe Syria does not need any military help from Iran.
"Unfortunately, the situation in Syria and the whole Middle East region is becoming more and more delicate and risky because of foreign interference and funnelling of arms to the extremist groups."
The diplomats also said that Iran Air and Mahan Air were well-known violators of the Iranian arms embargo.
Iran Air and Mahan Air were both mentioned in the intelligence report on Iranian arms shipments to Syria. The US Treasury Department has blacklisted Iran Air, Mahan Air and Yas Air for supporting Iran's Islamic Revolutionary Guards Corps.
"The equipment being transferred by both companies (Iran and Mahan Air) ... ranges from communications equipment to light arms and advanced strategic weapons, some of which are being used devastatingly by Hizbollah and the Syrian regime against the Syrian people," said the western intelligence report.
"The more sophisticated gear includes ... unmanned aerial vehicles, shore-to-sea missiles and surface-to-surface ballistic missiles," the report said. "Other weapons are being used by Syrian security forces, pro-Assad shabbiha militiamen and Lebanese Hizbollah."
There are about 5 tons of arms per flight, which are occurring on a near weekly basis, hidden in the bottom of the planes' fuselages, the report said, adding that arms cargo was removed separately after civilian cargo was unloaded.