UNITED NATIONS (Reuters) - The United Nations Security Council on Monday condemned North Korea's recent ballistic missile tests, warning that the launches contributed to the development of nuclear weapons delivery systems and were greatly increasing tensions.

North Korea fired a ballistic missile that landed in the sea near Russia on Sunday in a launch the United States called a message to South Korea days after its new president took office pledging to engage Pyongyang in dialogue.

In a unanimously agreed statement, the 15-member council said it was of vital importance that North Korea show "sincere commitment to denuclearisation through concrete action and stressed the importance of working to reduce tensions."

"To that end, the Security Council demanded the Democratic People's Republic of Korea conduct no further nuclear and ballistic missile tests," the council said, adding that it was ready to impose further sanctions on the country.

The statement also condemned an April 28 ballistic missile launch by Pyongyang.

Following that launch, Washington began talks with North Korean ally China on possible new U.N. sanctions. Traditionally, the United States and China have negotiated new measures before involving remaining council members.

The U.N. Security Council first imposed sanctions on North Korea in 2006 and has strengthened the measures in response to its five nuclear tests and two long-range rocket launches. Pyongyang is threatening a sixth nuclear test.

"The members of the Security Council vowed to fully implement all measures imposed on (North Korea) by the Security Council and strongly urge all other member states to do so in an expeditious and serious manner," the statement said on Monday.

North Korea made a global appeal in a letter released on Friday for states to reconsider enforcing U.N. sanctions on the Asian nation.

North Korea has in the past year stepped up its ballistic missile tests, firing dozens of various types of rockets, according to South Korea.

Experts said Sunday's successful launch signals major advances in developing an intercontinental ballistic missile, such as mastery of re-entry technology and better engine performance key to targeting the United States.

(Reporting by Michelle Nichols, editing by G Crosse and Mary Milliken)