Ukraine invasion: Russia's attack in maps

Russia has launched a major invasion of Ukraine from three main directions.

Reports say troops are advancing from the north in the direction of Kyiv; from the east through Donetsk, Luhansk and Kharkiv; and from Crimea in the south.

From approximately 03:00GMT, explosions were heard in many cities across the country, as Ukraine's air defences and other military infrastructure came under attack.

Analysts say that strikes from the air are aimed at clearing the way for ground troops to move in.

Among the targets were positions in Kyiv, Karkhiv and Odesa.

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, are thought to be moving towards Chernihiv, on a direct path to Kyiv.

Ukrainian officials say Russian helicopters have attacked a military airfield at Gostomel, west of Kyiv.

A missile strike also hit the town of Brovary, east of Kyiv.

Analysts say a Russian advance may avoid the exclusion zone around the Chernobyl nuclear power plant, which exploded in in 1986.

From the east, there are reports that Russian tanks have arrived in Kharkhiv, Ukraine's second-largest city.

Overnight, there were large explosions in Donetsk, and similar blasts coming from the direction of Belgorod across the border, where large troop movements were reported on Wednesday.

Separately, Russia's Interfax news agency reported claims from Russian-backed separatists that they had launched an offensive on the Ukrainian-controlled town of Shchastia in Luhansk.

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, troops have crossed from from Crimea to the mainland, towards Kherson, taking Chongar and Novo Alekseyevka.

Overnight, explosions were heard in cities across the region, including Odesa, Mariupol, Melitpol and Kherson.

Ukrainian officials - quoted by the Reuters news agency - said Russian troops had landed in the ports of Odesa and Mariupol.

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 and Mark Bryson