Iran has significantly stepped up military support to 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 said.

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 told Reuters on condition of anonymity. Iraqi and Turkish officials denied the allegations.

Iran’s acceleration of support for 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 Assad and offering Syria’s increasingly isolated government a crucial lifeline, the envoys said.

It also highlights the growing sectarian nature of the conflict, diplomats say, with Iranian arms flowing to the Shi’ite militant group Hizbollah. That group is increasingly active on the ground in Syria in support of Assad’s forces, envoys say.

The Syrian conflict started out two years ago as a pro-democracy movement. Some 70,000 people have been killed and more than one million refugees have fled the violence.

A Western intelligence report seen by Reuters in September said Iran was using civilian aircraft to fly military personnel and large quantities of weapons across Iraqi airspace to aid Assad.

Iraq denied that report but later made a point of inspecting an Iran-bound flight that it said had no arms on board. Much of the weaponry going to Syria now, diplomats say, continues to be shipped to Iran through Iraqi airspace and overland through Iraq, despite Baghdad’s promises to put a stop to Iranian arms supplies to Assad in violation of a UN arms embargo on Tehran over its nuclear programme.