By Louis Charbonneau

UNITED NATIONS (Reuters) - A U.N. Security Council committee on Wednesday added three "very significant" North Korean state companies to a U.N. blacklist of firms banned from international trade, U.S. Ambassador to the United Nations Susan Rice told reporters.

The decision by the Security Council's North Korea sanctions committee came after China consented to sanctions on the trio of companies. It falls far short of the roughly 40 firms the United States, European Union, South Korea and Japan had wanted to blacklist after Pyongyang's recent rocket launch.

The newly blacklisted firms are "very significant North Korean entities" involved in Pyongyang's nuclear and missile programs, Rice said.

China, North Korea's protector on the Security Council and a permanent veto-wielding member, had initially consented to sanction only two new companies but eventually agreed to blacklist one additional firm, council diplomats told Reuters on condition of anonymity.

The three companies are Green Pine Conglomerat, Amroggang Development Banking Corporation and Korea Heungjin Trading Company.

Diplomats attempted to play down the fact that Beijing had vetoed the vast majority of their proposed listings.

"This is exactly what we expected," a diplomat told Reuters. "We knew China would only agree to designate some of the entities. Of course we would have liked more, but it will still send a signal to North Korea that provocations are costly."

U.N. sanctions committees work on the basis of consensus, which means any individual council member can block agreement.

Last month, the council adopted a "presidential statement" that strongly condemned North Korea's April 13 rocket launch, called for adding names to the list of those hit by existing U.N. sanctions and warned Pyongyang of further consequences if it carried out another missile launch or nuclear test.

The U.N. North Korea blacklist includes individuals facing international travel bans and asset freezes, companies whose assets are to be frozen and goods that North Korea is not allowed to export or import.

Prior to Wednesday's additions the North Korean sanctions listed included eight companies and five individuals. North Korea is barred from importing nuclear and ballistic-missile technology as well as luxury goods.

The committee's move on Wednesday also expanded the list of goods North Korea is not allowed import, Rice said.

The Security Council imposed two rounds of sanctions on Pyongyang after its 2006 and 2009 nuclear tests.

(Reporting by Louis Charbonneau)