The Foreign Secretary has given a cautious welcome to a Russian move to pull troops out of Syria as the bloody conflict enters its fifth year.
Philip Hammond said President Vladimir Putin's announcement that the "main part" of Moscow's forces were being withdrawn could be "positive".
The comment came after Mr Putin told a meeting at the Kremlin that action to shore up Syrian premier Bashar Assad had been successful.
The shift has seemingly been timed to coincide with a fresh round of peace talks in Geneva.
Tuesday also marks the fifth anniversary of a first wave of anti-Assad protests widely held to have signalled the start of the Syrian uprising.
The ensuing civil war has since claimed more than 250,000 lives, displaced half of Syria's population and flooded Europe with refugees.
"I consider the mission set for the defence ministry and the armed forces on the whole has been accomplished," Mr Putin reportedly said on Monday.
"I am therefore ordering the defence ministry to begin the withdrawal of the main part of our military force from the Syrian Arab Republic from tomorrow."
Having tipped the balance in the civil war in Assad's favour, Russia is still expected to maintain a naval base and air base in the country.
Moscow has suggested that the Syrian president agreed with the decision.
Mr Hammond posted on Twitter: "Russian move could be positive - if part of real commitment to Syrian-led political transition & continuation of cessation of hostilities."
Moscow formally entered the conflict in September by launching air strikes in Syria in support of Assad's forces.
A partial ceasefire backed by the US and Russia was announced in February.
Labour MP Jo Cox, who has campaigned for more humanitarian action in Syria, said: "Russia appears for the first time to be using its influence over the Syrian regime.
"Russia now has a choice - to use its influence for good to help get to a just and lasting negotiated solution, or continue to prolong the suffering of the Syrian people."