TALLINN, Estonia - Estonian officials yesterday said they had begun exhuming a grave thought to hold the remains of Soviet soldiers killed in World War II, a day after the removal of a memorial on the site provoked widespread rioting by ethnic Russians.

About 15 people are buried at the small park adjacent to where the Bronze Soldier monument stood. The exact number of bodies and their identity are not known.

Lutheran and Russian Orthodox ceremonies were conducted before the excavations started. The site was covered by a white tent and surrounded by police officers, who kept the media and public far from the area.

About 50,000 Soviet soldiers are estimated to have died on Estonian territory while fighting Nazi German troops in World War II. Estonia's Russians - less than one-third of the country's 1.3 million population - regarded the monument as a shrine to Red Army soldiers who died fighting the Nazis, but ethnic Estonians consider it a painful reminder of hardships during a half-century of Soviet rule.

The Defense Ministry said it aimed to complete the excavation work "as quickly as possible" but did not give a time line.

The rioting was the worst seen since the Baltic state won independence from the Soviet Union in 1991, and has raised concern throughout the European Union, which Estonia joined in 2004.

President Vladimir V. Putin expressed the "most serious concern" about the "crisis situation" to German Chancellor Angela Merkel, whose country holds the rotating chairmanship of the European Union, the Kremlin said.

Foreign Minister Sergei Lavrov last week called the decision to remove the statue and graves "absolutely repulsive."

Sixty-six people were injured in Tallinn, including six policemen, as angry ethnic Russian youths rioted for a second night Friday. More than 500 people - many of them adolescents - were detained overnight as vandals prowled the streets, breaking shop windows and looting stores, police spokeswoman Julia Garanza said yesterday.

Unrest also spread to Kohtla-Jarve and Johvi, two towns dominated by ethnic Russians about 110 miles east of Tallinn. More than 40 people were detained there, local officials said.

The statue, of a Red Army soldier with his rifle slung over his back, was being held at an undisclosed location, said Andreas Kaju, a Defense Ministry adviser.