At least five people have died after heavy shelling in rebel stronghold Donetsk in eastern Ukraine damaged a hospital, six schools and five nursery schools.

The fighting between Russia-backed separatists and government troops in eastern Ukraine resumed in January after a month of relative calm, killing more than 200 people in the past three weeks, according to the United Nations.

As the conflict intensifies Ukrainian president Petro Poroshenko says he is confident that the United States will agree to send weapons to his country to help it fight pro-Russian rebels, a step the Americans are reportedly considering.

On a visit to a government-controlled city in eastern Ukraine on Tuesday, Mr Poroshenko said that his government badly needs the aid to help repel the separatist attacks in the conflict that that has left 5,300 people dead.

US president Barack Obama has opposed sending lethal assistance to Ukraine's government, but a senior administration official said the surge in fighting has spurred the White House to review the policy.

Mr Poroshenko will have an opportunity to make his case to US Secretary of State John Kerry on Thursday who is scheduled to visit Kiev.

"I don't have a slightest doubt that the decision to supply Ukraine with weapons will be made by the United States as well as by other partners of ours," he said on a visit to Kharkiv, "because we need to have the capabilities to defend ourselves."

Germany's chancellor Angela Merkel has said she is opposed to the idea.

In Kiev, two Ukrainian troops have been killed and 18 injured in the past 24 hours. The most intense fighting is now focused on the railway hub of Debaltseve where, according to Seleznev, the rebels mounted an offensive against Ukrainian troops.