Invading Russian forces press deep into Ukraine

Invading Russian forces pressed deep into Ukraine as deadly battles reached the outskirts of Kyiv, with explosions heard in the capital early Friday that the besieged government described as "horrific rocket strikes".

The blasts in Kyiv set off a second day of violence after Russian President Vladimir Putin defied Western warnings to unleash a full-scale ground invasion and air assault that quickly claimed dozens of lives and displaced at least 100,000 people.

The United States and its allies responded with a barrage of sanctions, but the Russian forces appeared intent Friday on pressing home their advantage after a string of key strategic victories on day one.

"Horrific Russian rocket strikes on Kyiv," Ukraine Foreign Minister Dmytro Kuleba posted on Twitter after explosions were heard in the capital before dawn.

"Last time our capital experienced anything like this was in 1941 when it was attacked by Nazi Germany. Ukraine defeated that evil and will defeat this one."

At least 137 "heroes" were killed during the first day of fighting, President Volodymyr Zelensky said on Thursday, as he called up conscripts and reservists nationwide to fight in a general mobilisation.

Zelensky said there was now a "new iron curtain" between Russia and the rest of the world, like in the Cold War, adding in a later speech his nation had been "left alone".

"Who is ready to fight alongside us? I don't see anyone."

And while the United States moved to impose sanctions on Russian elites and banks, it stressed that American forces would not head to eastern Europe to fight in Ukraine.

NATO said it had activated "defence plans" for allied countries.

But NATO chief Jens Stoltenberg said there was no plan to send alliance forces into Ukraine.