President Vladimir Putin put Russia's nuclear deterrent on high alert on Sunday (Feb 27) in the face of a barrage of Western reprisals for his war on Ukraine, which said it had repelled Russian ground forces attacking its biggest cities.

The United States said Mr Putin was escalating the war with "dangerous rhetoric", amid signs that the biggest assault on a European state since World War II was not producing rapid victories, but instead generating a far-reaching and concerted Western response.

The Russian rouble plunged nearly 20 per cent to a new record low versus the dollar on Monday in early Asian trade after Western nations on Saturday unveiled harsh sanctions, including blocking some banks from the Swift international payments system.

Meanwhile, Ukraine's health ministry has said 352 civilians, including 14 children, have been killed since the beginning of Russia's invasion.

Dr Malcom Davis from the Australian Strategic Policy Institute and ST mobile editor Jeremy Au Yong weigh in on these developments.

Get live updates as the Ukraine crisis unfolds.