Some 75 Russian ships, over 20 aircraft and around 30,000 troops and civilian experts have been conducting 10 days of exercises that will end Thursday, Russia's largest military manoeuvres for 15 years.

The submarines were spotted Saturday off the Primorye region coast and Monday near the Kamchatka peninsula, Admiral Vladimir Kuroyedov told reporters, without naming the countries they belonged to.

"We are in full control of the situation and are ready to cooperate with our observers," Kuroyedov said.

"These submarines are probably replacing the observers that certain countries did not send," he added.

Japan, the United States and North Korea declined to send observers for the naval maneouvres although civilian teams from Japan as well as South Korea did take part in a mock rescue operation of a ship on Monday.

Monday's joint drill saw participants tackle the consequences of a mock explosion on an ice-breaker. US ships had also been scheduled to take part, but their arrival was delayed by bad weather.

The only military exercise that attracted foreign observers was a wargame Monday that saw some 100 Islamic "terrorists" seize control of a coastal slice of territory on the Russian fareastern mainland.

Canadian, Chinese and South Korean military observers were present to see Russian marine and army paratroopers backed up by aircraft and navy vessels fight off the "terrorists" in the Primorye region neighbouring North Korea.

Russian Defence Minister Igor Ivanov, who was there to see the manoeuvre, one of 45 separate exercises in the 10-day wargames, defended the need to conduct them and denied that far eastern countries bordering Russia were concerned.

"When it is a question of fighting international or internal terrorism, nothing is impossible," he said.

WAR.WIRE