North Korea made a global appeal in a letter released on Friday for states to reconsider enforcing U.N. sanctions on the Asian nation as Washington seeks to step up pressure on Pyongyang to end its nuclear and ballistic missile programs.

The United Nations 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.

In the letter to 192 U.N. members and two observer states - dated Thursday - North Korea urged them to "reconsider any of their implementation activities until the legality of those 'sanctions resolutions' are to be clarified."

North Korea has repeatedly requested that an international forum of legal experts be established by the United Nations to clarify the legal basis for the U.N. sanctions.

The U.N. Security Council North Korea sanctions committee has been meeting with regional blocs at the United Nations to push for enforcement of existing sanctions and assist countries with questions on how to implement the measures.

In a press statement attached to its letter, North Korea's U.N. mission accused the United States of trying to intimidate countries into fully implementing U.N. sanctions by "openly threatening that they would be faced with 'strong measures of sanction' by the U.S."

North Korea argued that there would be no need for Washington to "beg or threaten" countries to implement the measures if the sanctions had a clear legal basis.

The United States is negotiating with Pyongyang ally China on strengthening U.N. sanctions. North Korea has in the past year stepped up its ballistic missile tests, firing dozens of various types of rockets, according to South Korea.

U.S. Secretary of State Rex Tillerson last month urged the Security Council to act before North Korea does.

North Korea also sent a rare letter of protest to the U.S. House of Representatives on Friday warning that a new package of tougher sanctions would only spur its development of nuclear weapons, North Korea's state media reported.

Last month, North Korea reconvened the Foreign Affairs Committee, which was abolished in the late 1990s, in what analysts saw as an attempt to improve relations with the outside world amid its deepening isolation.