The United States welcomes the ceasefire agreement on the Ukraine crisis reached in the Belarusian capital of Minsk and calls for immediate implementation of the deal, the White House said Thursday.

The leaders of Ukraine, Russia, Germany and France announced Thursday a peace deal for an end to fighting in eastern Ukraine following 14-hour marathon talks in Minsk.

The agreement represents a "potentially significant step" toward a peaceful resolution of the conflict and the restoration of Ukraine's sovereignty consistent with the Minsk agreements from last September, White House spokesman Josh Earnest said in a statement.

The agreement envisages a ceasefire between Ukrainian forces and independence-seeking insurgents starting Sunday, followed by the withdrawal of heavy weapons from the front line and constitutional reform to give eastern Ukraine more autonomy.

Earnest called on all parties to carry out the accord and the September agreements "fully and without delay."

"The true test of today's accord will be in its full and unambiguous implementation, including the durable end of hostilities and the restoration of Ukrainian control over its border with Russia," the spokesman said.

In the statement, the White House also expressed its concerns about the escalation of fighting in eastern Ukraine Thursday, which it said "is inconsistent with the spirit of the accord."

Heavy weapons must be withdrawn from the conflict zone, and Russia must end its support for the separatists and withdraw its soldiers and military equipment from eastern Ukraine, Earnest said.

The summit of peace talks that began Wednesday has been considered as the high point of intensive multilateral efforts aimed at finding a way out of the crisis in Ukraine, where more than 5,300 people have been killed since April last year.