Britain has requested Cyprus to reserve airspace in its air traffic control region in preparation for potential Western military strikes in retaliation for a suspected chemical attack by Syrian government forces on the insurgent-held town of Douma.
Increased airspace would provide for heightened activity at Britain's air base at Akrotiri on the island, which was used during the 1991 and 2003 US-led wars to mount attacks on Iraq. The UK request was for a period of a few weeks.
Anticipating Western military action, Syrian warplanes and helicopters have moved to Russian bases, army personnel have dispersed and an offensive has been postponed against Isis in the last jihadi pocket in Damascus’s southern suburbs.
Britain and France have agreed to join a US-led campaign, but deliberations continue over the extent of strikes and targets.
More time before any strikes has been made available by the arrival in Damascus of experts from the Organisation for the Prohibition of Chemical Weapons, which will inspect sites in Douma where chemical agents were said to have been used a week ago.
This mission has given the sides a chance to reflect and, perhaps, with input from Russia, select targets. Over the past few days the "deconfliction hotline" between the US and Russian militaries has been buzzing in an effort to avert a clash involving the west and Russia.
Arguing the Syrian army is guilty of using banned chemical agents, the Western powers intend to inflict retribution to deter Damascus from employing such weapons again.
Moscow, which claims chemical weapons have not been used, has threatened to respond by striking Western aircraft, ships and launch sites if Russians deployed in Syria are killed or wounded.
Russia also warned it could retaliate against strikes that degrade Syrian government forces which have over the past two years clawed back territory from insurgents and jihadis.
There is a precedent for consultation designed to prevent confrontation. Last April, before firing 59 cruise missiles at an airbase following a nerve gas attack in northwestern Syria, the Trump administration told Russia that its bases and troops would not be hit.
However, that was a one-off strike. The US has suggested a coming attack could involve multiple attacks on a range of sites. Russian sources predicted eight without specifying which.
Among the possible targets are research facilities related to the manufacture of chemical weapons, command centres, security headquarters, and the Dumair air base near Damascus from which the opposition claims chemical strikes on Douma were launched. Israel has previously hit these scientific sites.
There are 25 air bases in Syria, 20 of them under government control.
Russia has exclusive use of the Hmeimim air base and the Tartus naval facility in Latakia province on the Mediterranean, but has advisers and technical staff at half the bases operated by the government, notably those with radar and anti-missile installations which could counter a tripartite attack.
Iran is also concerned about the safety of its military personnel and pro-Iran Shia militiamen deployed in Syria. Tehran has warned it will retaliate for the deaths of seven Iranian officers at the T-4 airbase bombed by Israel last week.
The US has a large military base near the town of Tabqa in the north, a major air base in Hasaka province in the northeast, an insurgent-training facility at Tanf in the southeast and more than half a dozen airstrips and military facilities planted in the Kurdish-occupied north, where Britain, France and Germany also have troops.
These facilities could suffer retaliation from Russian, Iranian or Syrian forces, risking escalation both sides say they seek to avoid.