Boris Johnson has pulled out of a visit to Moscow in the wake of the Syrian chemical weapons attack saying "we deplore Russia's continued defence of the Assad regime".
The Foreign Secretary was due to visit Russia on Monday for talks with counterpart Sergey Lavrov, which would have been the first visit by a UK foreign secretary in more than five years.
But Mr Johnson attacked the Kremlin and said he would instead focus on building support with allies to secure a ceasefire in war-torn Syria.
"We deplore Russia's continued defence of the Assad regime even after the chemical weapons attack on innocent civilians," he said.
"We call on Russia to do everything possible to bring about a political settlement in Syria and work with the rest of the international community to ensure that the shocking events of the last week are never repeated."
Mr Johnson had originally planned to fly out to Moscow at the end of March, but rescheduled the visit in order to attend a meeting with Nato counterparts, including US secretary of state Rex Tillerson.
Russia has condemned US missile strikes on an airbase at Shayrat as an act of "aggression against a sovereign state in violation of international law".
Mr Tillerson will still go ahead with a visit to Moscow to deliver a "clear and co-ordinated" message to the Russians, Mr Johnson said.
"Developments in Syria have changed the situation fundamentally," he said.
"My priority is now to continue contact with the US and others in the run-up to the G7 meeting on 10/11 April - to build co-ordinated international support for a ceasefire on the ground and an intensified political process.
"I will be working to arrange for other like-minded partners to meet and explore next steps soon, too.
"I discussed these plans in detail with Secretary Tillerson. He will visit Moscow as planned and, following the G7 meeting, will be able to deliver that clear and co-ordinated message to the Russians."