Russian chess grandmaster Anatoly Karpov has been unable for several months to obtain a visa to travel to the United States, his friend, the owner of a chess academy in New York who invited him to teach a summer camp there, said on Wednesday.

Karpov, 68, considered one of the greatest chess players of the modern era, has visited the United States regularly since 1972. He first applied for the non-immigrant visa in March and is still waiting for it to be approved, said Maxim Dlugy of the Chess Max Academy.

"He was suddenly called in for an interview in the Moscow embassy and asked, "Are you going to talk to U.S. Senators and Congressmen? We'll have to check that out'," Dlugy said.

Staff members of U.S. Representative Carolyn Maloney and U.S. Senator Chuck Schumer both contacted the U.S. Embassy in Moscow on Karpov's behalf and were told that his application was still being processed.

"This processing cannot be waived or expedited as it is crucial for the final decision regarding the issuance of a visa," the embassy's public liaison unit said in a July 2 letter to Maloney's office.