Russian missiles strike Lviv

U.S. President Joe Biden was due to talk with Chinese president Xi Jinping later on Friday, in an attempt to starve Russia's war machine by isolating Moscow from the one big power that has yet to condemn its assault.

More than three weeks since President Vladimir Putin launched an invasion to subdue what he calls an artificial state undeserving of nationhood, Ukraine's elected government is still standing and Russian forces have not captured a single big city.

Russian troops have taken heavy losses while blasting residential areas to rubble, sending more than 3 million refugees fleeing. Moscow denies it is targeting civilians in what it calls a "special operation" to disarm its neighbour.

"Russian forces have made minimal progress this week, Britain's," defence ministry said in a daily military intelligence update.

"Ukrainian forces around Kyiv and Mykolaiv continue to frustrate Russian attempts to encircle the cities. The cities of Kharkiv, Chernihiv, Sumy and Mariupol remain encircled and subject to heavy Russian shelling."

At least three blasts were heard near Lviv's airport on Friday morning, with videos on social media showing large explosions and mushroom-shaped plumes of smoke rising.

Lviv's mayor, Andriy Sadovy, said several missiles has struck an aircraft maintenance facility, destroying buildings but causing no casualties.

The city, in Western Ukraine near the Polish border, is hundreds of miles from Russia's advance and has been one of the main destinations for Ukrainians forced to flee battle zones.

Russia has stepped up missile attacks on scattered targets in western Ukraine in recent days in what Ukrainian officials see as a bid to widen the conflict beyond areas where their troops are now bogged down.