Diplomats say the U.N. Security Council is prepared to impose new, tougher sanctions on North Korea over its fifth and largest nuclear test yet.

U.S. officials who declined to be identified because the Security Council resolution has not yet been made public said Monday that if the text is adopted and fully implemented it would mark "a significant step forward," in the sanctions regime against North Korea over its nuclear program.

Officials said they expect the council to vote on the resolution, which for the first time places a hard cap on North Korean coal exports, on Wednesday morning.

The U.S. and other veto-wielding permanent council members — Russia, China, Britain and France — have been negotiating the new sanctions for months in response to North Korea's Sept. 9 nuclear test.