Fighting has reached the Ukrainian capital Kyiv after Russians launched a full-scale invasion of the country from three main directions.

Troops are advancing from the north; from the east through Donetsk, Luhansk, Kharkiv and Sumy; and from Crimea in the south.

Dozens of targets have been struck, as Russian troops have poured into Ukraine and launched missile strikes on major cities.

Russian troops arrived in the Obolon district of Kyiv on Friday, less than 6 miles (9km) from the city centre.

Overnight, explosions rocked the city and there were reports of fighting near the zoo and Shuliavka neighbourhood in the west of the city in the early hours of Saturday.

The city's mayor, Vitali Klitschko, said there was no major Russian military presence in Kyiv, but he said Russian saboteur groups were active.

A residential apartment building was hit by a missile as the capital came under attack.

Ukrainian troops are reported to have repelled an attack on Peremohy Avenue, but reports suggest the Russians are also continuing to advance from Ivankiv to the north west.

The Ukrainian army had tried to slow the Russian advance by blowing up a bridge over the Teteriv river at Ivankiv, 50 miles (80km) to the north of the city.

There has been fierce fighting at Hostomel airport, to the west of Kyiv, which was attacked by airborne Russian troops.

Russia is now in full control of significant parts of Ukraine's territory.

After Ukraine's air defences and other military infrastructure came under attack on Thursday, columns of tanks moved rapidly into position, backed up by artillery and air power.

Among the initial targets were Kyiv, Karkhiv, Odesa and Ivano-Frankivsk.

Troops are now spreading out in parts of the north, east and south, with missile strikes and artillery clearing the way for advancing Russian forces.

From the north, Russian troops are believed to have crossed the border into Ukraine at the three-way junction between Ukraine, Russia and Belarus, at Senkivka.

In recent weeks, a huge deployment of Russian troops has gathered close to Novye Yurkovichi and Troebortno, including "the entire 41st army", according to Michael Kofman of the US-based Center for Naval Analyses.

Armoured columns, including tanks and multiple launch rocket systems, moved towards Chernihiv. But reports suggest their advance from Chernihiv to Kyiv has been held back by Ukrainian forces.

A second advance has come down the west side of the Dnieper river via Chernobyl.

In the east, there has been fighting around Kharkhiv, Ukraine's second-largest city. Parts of the city have been shelled.

There is also fighting around Donetsk, which has come under attack from troops crossing from Belgorod in western Russia.

There are thought to be about 15,000 Russian-backed separatists in Donetsk and Luhansk, who may help a Russian advance. Ukraine believes the figure is higher.

In the south, Russian troops have crossed from Crimea to the mainland taking Chongar and Novoalekseyevka and there has been heavy fighting around Kherson.

The Ukrainian military says areas near the cities of Poltava and Mariupol have been hit by Russian cruise missiles launched from the Black Sea.

Explosions have also been heard in Odesa and Melitpol. The Russian defence ministry claims its troops entered Melitopol without resistance - although western officials suggest it is still in Ukrainian hands.

There are reports of heavy fighting near the port Mariupol.

The Pentagon says that Russian forces have conducted an amphibious assault to the west of the city. An advance from Mariupol to the east would create a land bridge between Crimea and territory held by pro-Russian separatists in Donetsk and Luhansk.

In recent days, Russia had positioned landing ships capable of deploying main battle tanks, armoured vehicles and personnel, off the Ukrainian coast in a major build-up in the Black Sea and the Sea of Azov.

Ukrainian forces are concentrated in the east of Ukraine, towards Donetsk and Luhansk,

Ben Barry, of the International Institute for Strategic Studies, says that a Russian advance north from Crimea may succeed in cutting them off from Kyiv, stranding them on the east side of the Dnieper River.

With Russian troops to their east, in Donetsk and Luhansk, north in Russia, and on the west bank of the Dnieper, they would be encircled.

Graphics by Zoe Bartholomew, Mark Bryson and Sana Dionysiou