The map of Ukraine showing the advance of Russian troops towards Kyiv

(CNN) — Some Russian forces advanced south from positions in Belarus, where they were present for “joint military exercises”.

Despite resistance from the Ukrainian military, Russian troops reportedly entered the Obolon district of northern Kyiv on Friday morning.

A battle is underway for control of Ukraine’s capital, Kyiv, and explosions have been heard throughout the night. The United States has warned that Russia is trying to surround the city, and a Ukrainian official said the city has been hit by missiles.

Some 18,000 weapons with ammunition have been distributed to reservists in the Kyiv region alone and all men between the ages of 18 and 60 are banned from leaving Ukraine.

There are reports of heavy fighting between Russian and Ukrainian forces around the city of Chernihiv, some 105 kilometers (about 65 miles) north of the capital of Kyiv.

A video from the city showed the regional headquarters of the Security Service of Ukraine in flames. A witness contacted by CNN said he was still burning Friday night.

The Russian Defense Ministry has acknowledged the fighting in the area, saying Russian forces “have completed the blockade of the city of Chernihiv”, essentially cutting off the tracks.

Ukraine says its forces inflicted heavy losses on Russian columns around Chernihiv, destroying more than 30 tanks.

Earlier Friday, the head of the Ukrainian armed forces, Valerii Zaluzhnyi, said that the Ukrainian army had managed to maintain the defense and repel the advancing Russian troops in Chernihiv.

See on this map the advance of Russian troops towards Kyiv