(Reuters) - Ukrainian government forces said they had suspended combat operations as a "Day of Silence" began in the war-torn east on Tuesday, marking an effective ceasefire on the front line of the conflict with separatist rebels.

In the city of Donetsk, the separatists' main stronghold, a Reuters correspondent said firing was heard up to 9 a.m. but later appeared to have slackened off.

"The Ukrainian military have suspended all combat actions and are ready for the Day of Silence, but if separatists attack we will fire in response," a military spokesman said by telephone.

The Ukrainians have billed the Day of Silence a litmus test for the readiness of Russian-backed separatists to reinforce a ceasefire which was agreed three months ago but which has been regularly breached with almost daily deaths among government forces, civilians and rebels.

If it holds, it could improve prospects for a renewal of peace talks in the Belarussian capital Minsk later this week involving Russia, Ukraine and separatist leaders under the auspices of the Organization for Security and Cooperation in Europe.

It was in talks by the so-called contact group in Minsk in early September that a 12-point blueprint for peace, including a ceasefire, was worked out.

But much has changed in eastern Ukraine since then. The separatists have declared "people's republics" and elected officials, while on the battlefield, separatist assaults have continued on the main international airport in Donetsk to wrest control from government forces.

Ukraine also accuses Russia of failing to withdraw fighters and military equipment as agreed in September.

The United Nations says more than 4,300 people have been killed in eight months of conflict which has driven relations between Russia and the West to the lowest since the Cold War.

In Moscow, Russian Foreign Minister Sergei Lavrov expected a meeting of the contact group soon. "In the coming days, a meeting of the contact group is planned, in which will be discussed a plan ... with the aim of a final ceasefire," RIA news agency quoted him as saying.

The Kiev military said separatist attacks had continued in the past 24 hours up to the start of the Day of Silence. "In the past 24 hours, the bandits carried out 64 attempted attacks on positions of Ukrainian forces," a military statement said.

Two civilians had been killed and 10 others wounded "as a result of sudden artillery fire by (separatist) fighters on populated areas," it said.