Russia has enough troops ready to take Kyiv, says former Ukraine defence chief

US officials have warned that a full attack could lead to the swift capture of Kyiv and potentially result in 50,000 civilians killed or wounded, as well as up to 25,000 dead Ukrainian soldiers and 10,000 Russian ones. Millions could flee in a refugee crisis for Europe, they suggested.

The latest US assessment was shared late last week with House and Senate representatives in closed briefings. Putin had not made a final decision to invade, US intelligence analysts indicated. But they pointed to satellite images and communications among Russian forces that showed Moscow was in a position to carry out the largest military operation on land in Europe since 1945.

From Thursday, Russia will stage major military exercises with Belarus, within striking distance of Kyiv. According to the Nato secretary general, Jens Stoltenberg, Russia has deployed 30,000 combat troops, elite Spetsnaz units, Su-35 fighter jets and S-400 missile defence systems.

Russia has moved troops into Crimea, in the south, which Putin annexed in 2014. Its forces have been positioned in a way that suggest Russia could invade from three sides, the US thinks.

US officials briefing on Saturday said 14 battalion tactical groups were on their way to the border from other parts of Russia. The US believes the Kremlin would want between 110 and 130 battalion tactical groups for use in a full-scale invasion, but also says Putin could decide on a more limited incursion.

Including support units, Russia could be aiming to have 150,000 troops in place for a full-blown military offensive, one US official said, adding that the buildup could reach that level in the next couple of weeks.

In Washington, efforts in Congress to impose economic punishment on Russia also appear to be growing. John Barrasso, the Republican ranking member of the Senate foreign relations committee, said on Sunday that it was clear that Putin alone would make the decision to invade.

Ben Cardin, a Democratic senator for Maryland and a senior committee member, said there were differences with Republicans over the content and timing of the sanctions package, but that he expected a bill to be presented to the House of Representatives soon.