Russia widened its military offensive in Ukraine on Friday, striking near airports in the west of the country for the first time, as observers and satellite photos indicated that its troops, long stalled in a convoy outside the capital Kyiv, were maneuvering in an attempt to encircle the city.

The U.S. and its allies prepared to step up their efforts to isolate and sanction Russia by revoking its most favored trading status. But with the invasion now in its third week, the new moves on the ground pointed to Russia forces trying to regroup, bombarding new cities as they tightened their 10-day-old siege on the key Ukrainian port city of Mariupol, where tens of thousands were struggling to find food.

The new airstrikes in western Ukraine were likely a message from Russia that no area was safe. Western and Ukrainian officials have said the Russian forces have struggled in the face of heavier-than-expected resistance and supply and morale problems. So far, they have made the most advances on cities in the south and east while stalling in the north and around Kyiv.

Russian forces bearing down on Kyiv are regrouping northwest of the Ukrainian capital, satellite pictures showed, in what Britain said could be preparation for an assault on the city within days.

Ukraine accused Russian forces of hitting a psychiatric hospital near its eastern town of Izyum on Friday, in what the regional governor called "a brutal attack on civilians". Emergency services said no one was hurt as the patients were already sheltering in the basement. 

Reuters could not immediately verify the report and there was no immediate comment from Moscow.

Russia has been pounding Ukraine's cities while its main attack force north of Kyiv has been stalled on roads since the invasion's early days, having failed in what Western countries say was an initial plan for a lightning assault on the capital.

Images released by private U.S. satellite firm Maxar showed armoured units manoeuvring in and through towns close to an airport on Kyiv's northwest outskirts, site of intense fighting since Russia landed paratroops there in the first hours of the war.