By Jon Herskovitz

SEOUL (Reuters) - North Korea fired three short-range missiles off its west coast on Friday, the South's Yonhap news agency cited government officials as saying, on a day Pyongyang's media also launched a tirade of abuse at President Lee Myung-bak.

"... it appears the firing of the missiles was part of a regular exercise to check the performance," Yonhap quoted an unnamed South Korean Defence Ministry as saying on Saturday.

A similar launch in March riled regional tensions and was seen by analysts as a display of anger at Washington and Lee's new conservative government in Seoul.

North Korea has more than 1,000 missiles, at least 800 of them ballistic, that can hit all of South Korea and most parts of Japan, experts have said. Its launches often coincide with periods of political tension.

In Singapore on Saturday on the sidelines of a regional security meting, South Korean Defence Minister Lee Sang-hee told reporters he could neither confirm nor deny reports of the missile tests.

South Korea usually tries to downplay short-range missile launches as part of regular North Korean military drills.

North Korea on Friday unleashed a torrent of insults at President Lee, who took office in February on a promise to cut the free flow of aid Pyongyang has seen under liberal presidents who ruled for 10 years before.

Its communist party newspaper Rodong Sinmun denounced the Lee government's policy of linking aid to progress North Korea makes in ending its nuclear weapons programmes in international disarmament talks.

"(It) is a criminal move to cover up their true colours as sycophantic traitors keen on confrontation with the North, stem the trend of the times towards independent reunification and peace and prosperity and reduce the inter-Korean relations to a plaything of outside forces," the paper said.

Experts said North Korea has developed an arsenal of short-range missiles capable of attacking the capital Seoul, South Korean bases near their heavily armed border and U.S. troops stationed in South Korea to support the country's army.

Over the past few days, the chief U.S. and South Korean envoys in six-country talks aimed at ending the North's nuclear arms ambitions have met the North's chief envoy in Beijing.

North Korea missed an end of a 2007 deadline to provide a full accounting of its atomic arms programme as called for in a six-way deal. If it makes the declaration, the impoverished state can receive aid and be removed from a U.S. terrorism blacklist.