* U.S. general says Russian patrols up "drastically"
* Says flights aim to show capability, conduct surveillance
* Russian official dismisses Ukraine link (Updates with Russian Defence Ministry comment)
WASHINGTON, May 5 (Reuters) - Russia has increased its air activity over the Pacific Ocean since the start of the Ukraine crisis, including flights near the California coast and the U.S. Pacific island of Guam, the head of U.S. air forces in the Pacific said on Monday.
General Herbert "Hawk" Carlisle said the number of long-range Russian patrols around the Japanese islands and Korea had also increased "drastically" and there had been "a lot more ship activity as well".
"We relate a lot of that to what's going on in the Ukraine," Carlisle said at Washington's Center for Strategic and International Studies think tank.
Carlisle showed a slide of a U.S. F-15 fighter jet intercepting a Russian "Bear" aircraft, the Cold War NATO name for Russia's Tupolev Tu-95 strategic bomber, over Guam.
"Certainly what's going on in Ukraine and Crimea is a challenge for us and it's a challenge for us in Asia Pacific as well as Europe," Carlisle said.
Russia's state-run news agency Itar-Tass quoted an unidentified senior ministry official as saying the flights were not sabre-rattling and had nothing to do with Ukraine.
"To consider Russian air force flights over neutral Pacific Ocean waters a challenge to the United States is strange to say the least," Itar-Tass quoted the official as saying.
Carlisle said Russian flights in the area were aimed "to demonstrate their capability to do it" and to gather intelligence, adding that the surveillance had included observation of military exercises involving U.S. forces in South Korea and Japan.
"There are things that are concerning with respect to how they operate and how transparent they are with other nations in the vicinity," he said of Russia.
Carlisle gave no details of the incidents and the Defense Department and the U.S. Air Force and Navy in the Pacific did not immediately respond to a request for more information.
Mike Green, senior vice president for Asia at the Center for Strategic and International Studies, a Washington-based think tank, said the frequency of incidents was up and described them as being "evocative of the Cold War".
Russian President Vladimir Putin announced in 2007 that Russia was resuming sorties by its strategic bomber aircraft near NATO airspace that were suspended in 1992 after the collapse of the Soviet Union.
Putin, who made the announcement during a joint military exercise with China, said the move was necessary to guarantee Russia's safety and that other nations had not followed Moscow's example in suspending such flights. (Reporting by David Brunnstrom; Additional reporting by Vladimir Soldatkin in Moscow; Editing by Peter Graff)