BERLIN -- Police in Berlin began an intensive search Friday, dragging a lake and combing gardens with sniffer dogs, in the hope of finding a Russian artist who disappeared a week ago.

Police spokesman Bernhard Schodrowski said five divers searched a lake near Anna Mikhalchuk's home, and more than 80 officers with sniffer dogs swept through nearby gardens and along train tracks over several hours. They failed to turn up any trace of her.

"This [search] was part of the regular criminal investigation," Schodrowski said. "The police start their search where they lose track of a missing person."

Schodrowski said efforts to find Mikhalchuk, 52, would continue.

Also known in Russia by the name Anna Alchuk, Mikhalchuk left her apartment on March 21 and has not been seen since. She moved to Berlin with her husband, Mikhail Ryklin, in November 2007.

In 2005, she was acquitted by a Moscow court on charges of inciting religious hatred for her works in a controversial art exhibit condemned by the Russian Orthodox Church.

The 2003 exhibit -- titled "Caution, Religion" -- was organized by the Sakharov Museum.

Ryklin sent a letter to Berlin police on Saturday, asking them to intensify the search for his wife.

The Berlin Tagesspiegel daily wrote that Mikhalchuk is Jewish and quoted Ryklin as writing that his wife had received several anonymous threats in the past. Ryklin teaches at Humboldt University.