Each Side Says the Other Broke Truce in Karabakh : Ethnic conflict: Fresh fighting erupts as plans for peacekeeping are disclosed in Helsinki.

The warring sides in the four-year conflict over Nagorno-Karabakh accused each other Thursday of breaking a truce as the 52-nation European security summit in Helsinki, Finland, announced plans to send observers and later peacekeepers to the disputed enclave.

Fresh fighting in the mountainous region, populated mainly by Armenians but given by Moscow in 1923 to the former Soviet republic of Azerbaijan, has claimed the lives of 40 Azerbaijanis and 15 Armenians, according to Armenian sources. They said the violence started with an Azerbaijani attack.

But Azerbaijan’s Foreign Ministry said the latest Azerbaijani attack did not violate the cease-fire because it stopped before the truce took effect.

“Azerbaijan pledged to stop all military actions starting 1 a.m. July 9 and is keeping its promise,” said Gavril Kocharli, an official at the Azerbaijani Foreign Ministry. “We are waiting for an Armenian reaction. . . . We do not know if they will abide by (the cease-fire).”

The Azerbaijan Foreign Ministry asserted that Armenia violated the truce by firing artillery at Azerbaijani villages all day Thursday.

Armenians and Azerbaijanis have been locked in a violent conflict for four years, and an estimated 2,000 people have been killed in warfare between the two former Soviet republics.

The Conference on Security and Cooperation in Europe, meeting in Helsinki, decided to send observers to Nagorno-Karabakh to obtain a firm cease-fire and then peacekeepers to uphold the truce. Conflict-solving and peace missions will be a new role for the CSCE, created in 1975 to ease East-West tensions.

During its two-day summit, the group plans to broaden its activity to include peacemaking efforts in the former Soviet Bloc, which is plagued by ethnic violence.

When told of the European peace plans, Armenian officials at a Moscow news conference said they approved of them.

Boris Arushanyan, deputy chairman of the council of ministers of Nagorno-Karabakh, said that to do any good, peacekeeping troops should be heavily armed and posted on the border between Nagorno-Karabakh and Azerbaijan.