'US will respond decisively if N-arms used in Ukraine

Russia's military campaign has killed tens of thousands and left some Ukrainian cities wastelands

WASHINGTON/KYIV: The United States would respond decisively to any Russian use of nuclear weapons against Ukraine and has spelled out to Moscow the "catastrophic consequences" it would face, US national security adviser Jake Sullivan said on Sunday.

Sullivan's remarks represented the latest American warning following the thinly veiled nuclear threat made by Vladimir Putin last Wednesday in a speech in which the Russian president also announced his country's first wartime military mobilisation since World War Two.

"If Russia crosses this line, there will be catastrophic consequences for Russia. The United States will respond decisively," Sullivan told NBC's Meet the Press programme.

Sullivan did not describe the nature of the planned US response in his comments on Sunday but said the United.

States has privately to Moscow "spelled out in greater detail exactly what that would mean".

Sullivan said that the United States has been in frequent, direct contact with Russia, including during the last few days to discuss the situation in Ukraine and Putin's actions and threats.

Russia, Ukraine trade barbs over attacks

Ukraine and Russia traded accusations on Sunday of attacks on civilians in the southern Ukrainian cities of Odesa and Kherson as Russia sought to justify its seven-month war, even as it escalates with reinforcements and the expected annexation of regions its troops have seized.

Ukraine and Western countries say referendums on joining Russia in territories Russia has captured are a sham designed to justify their annexation and the ramping up of hostilities with newly drafted troops after recent battlefield losses.