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 manoeuvring in an attempt to encircle the city.

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The US and its allies prepared to step up their efforts to isolate and sanction Russia by revoking its most favoured 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.

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Strikes on the western Lutsk airfield killed four Ukrainian servicemen and wounded six, according to Lutsk Mayor Ihor Polishchuk. In Ivano-Frankivsk, residents were ordered to shelters after an air raid alert, Mayor Ruslan Martsinkiv said.

Russian Defence Ministry spokesman Igor Konashenkov said Russia used high-precision long-range weapons Friday to put military airfields in Lutsk and Ivano-Frankivsk “out of action.” He did not provide details.

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In another potentially ominous movement, new satellite photos appeared to show that the massive Russian convoy outside the Ukrainian capital had fanned out into nearby towns and forests.

Howitzers were towed into positions to open fire, and armoured units were seen in towns near the Antonov Airport north of the city, according to Maxar Technologies, the company that produced the images.

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The 40-mile (64-kilometre) line of vehicles, tanks and artillery had massed outside Kyiv early last week. But its advance had appeared to stall amid reports of food and fuel shortages while Ukrainian troops also targeted it with anti-tank missiles.