Fierce fighting continued in parts of Ukraine early Saturday, with Ukrainian authorities reporting Russian rocket fire on several major cities in the south of the country.

In the city of Dnipro, two or three heavy explosions were heard on Saturday night, the Ukrayinska Pravda portal reported, citing the regional administration.

The area around the city of Kryvyi Rih was shelled with rocket launchers. A gas station caught fire, said the head of the local military administration, Oleksandr Vilkul.

Vilkul said Russian forces used Grad multiple rocket launchers.

Like all reports from the combat zones, the information was not independently verifiable.

The port city of Odessa on the Black Sea was also hit with rockets on Friday evening.

Ukrainian President Volodymyr Zelenskyy said he expected violent Russian attacks in the east of his country. "Russian soldiers are being brought to Donbass. Likewise in the direction of Kharkiv," said the head of state in a video address. "The situation in the east of our country remains very difficult," he added.

Diplomatic efforts are expected to continue on Saturday. U.S. diplomat Victoria Nuland, the undersecretary of state for political affairs, is coming to Europe to coordinate the response to Russia's violent crackdown on its neighbor.

Nuland is expected to visit France, Germany, Turkey, Greece and Cyprus, the United States State Department said in Washington.