KYIV, 26 Feb (REUTERS) -- Russian and Ukrainian forces clashed on the outskirts of the Ukrainian capital on Saturday (Feb 26) as authorities urged citizens to help defend the city from advancing Russian forces in the worst European security crisis in decades.

Heavy, frequent artillery fire and intense gunfire, apparently some distance from the city centre, could be heard in Kyiv in the early hours, a Reuters witness said. The Ukrainian military said Russian troops attacked an army base on a main Kyiv avenue but the assault was repelled.

But even as the fighting grew more intense, the Russian and Ukrainian governments signalled an openness to negotiations, offering the first glimmer of hope for diplomacy since Russian President Vladimir Putin launched the invasion on Thursday.

"The fate of Ukraine is being decided right now," Ukrainian President Volodymyr Zelenskiy said on Friday in a video address posted to his Telegram channel. "Tonight, they will launch an assault. All of us must understand what awaits us. We must withstand this night."

The air force command reported heavy fighting near the air base at Vasylkiv southwest of the capital, which it said was under attack from Russian paratroopers.

It also said one of its fighters had shot down a Russian transport plane. Reuters could not independently verify the claims.

Kyiv residents were told by the defence ministry to make petrol bombs to repel the invaders, as witnesses reported hearing artillery rounds and intense gunfire from the western part of the city.