Russian air force fighters forced a U.S.-registered Lockheed C-130 Hercules cargo plane to land in the southern airport of Adler near the town of Sochi on Tuesday after it violated Russian airspace, Itar-Tass news agency said. The plane, on a trip from Frankfurt to the Georgian capital Tbilisi, was later allowed to continue its trip after the crew had been interrogated. Tass said First Deputy Foreign Minister Anatoly Adamshin had told the U.S. ambassador, Thomas Pickering, that the plane was forced to land at 2.10 P.M. (1030 GMT) after penetrating 80 kilometers into Russian airspace without permission. The crew earlier ignored warnings they were about to enter Russian airspace. "We consider disciplinary measures should be taken ... and that all should be done to prevent such dangerous incidents from taking place in future," Adamshin told Pickering. The U.S. ambassador in turn expresed thanks to the Russian side for "showing tact and understanding" and letting the Hercules continue on to Tbilisi, Itar-Tass reported. A duty officer at the American embassy said he was unaware of the report. Neither the Russian Air Defense Forces nor the Defense Ministry were available for comment. In April Russian fighter planes forced an Israeli private aircraft to land at Adler after it violated Russian airspace on a flight from Tbilisi to Tel Aviv. Seven years ago the Air Defense Force came under heavy criticism and its chief was sacked after a West German citizen, Mathias Rust, flew a light aircraft over the Soviet Union's northern frontiers and landed it on Red Square in May 1987. More recently, the force's effectiveness has been put in question by the loss of forward tracking stations in Ukraine and the former Soviet Transcaucasus republics.