UNITED NATIONS, May 27 (Reuters) - The United Nations' International Civil Aviation Organization (ICAO) agreed on Thursday to investigate the forced grounding of a Ryanair (RYA.I) passenger plane in Minsk, an incident that prompted international outrage.

ICAO's 36-nation governing council acted after the United States and several allies demanded an investigation into the incident, which British Foreign Secretary Dominic Raab called "a grave violation of international law."

ICAO would produce an interim report by June 25, said Irish Transport Minister Eamon Ryan. ICAO said in a statement after the meeting that its council had expressed its "strong concern" about the incident.

The probe will be a fact-finding investigation designed mainly to determine whether international aviation rules were breached. ICAO has little scope to punish member states other than by suspending voting rights.

Belarus on Sunday scrambled a fighter and used a false bomb alert to divert the Irish airliner to Minsk and detain a dissident Belarusian journalist. The plane, traveling from Athens to Vilnius, was almost in Lithuanian air space when ordered to land.

"These unacceptable actions were an attack on European aviation security and put in danger the lives of the passengers and crew as they traveled between two EU capitals," said Ryan.

Minsk, now facing calls for sanctions, rejected charges it acted illegally and accused the West of using the episode to wage "hybrid war" against it.

The council urged ICAO members to cooperate with the probe.

"They could not just close their eyes," one person familiar with the meeting said, adding safety had been a key topic.

Two sources familiar with the meeting said Russia and China had both declined to support an investigation.

Russia, which has accused the West of hypocrisy, told delegates that what happened in Minsk was not an isolated incident and recalled reports that Washington had caused a jet thought to be carrying fugitive Edward Snowden to land in Austria in 2013, the sources said.

China argued for more time before taking action, one added.

Russian and Chinese diplomats did not immediately respond to requests for comment.

Montreal-based ICAO wields clout through its safety and security standards, which are approved by its 192 member states.

"We wish to remind those who demanded we take punitive action against that country that our agency was never assigned that type of role or capability," ICAO tweeted on Wednesday.

Belarus told the meeting the airliner had not been forced down by authorities and that the pilot could have landed in Lithuania, said a source familiar with what happened. The source requested anonymity given the sensitivity of the situation.

Under the Chicago Convention, each country has sovereignty over its own air space, but the treaty prohibits any use of civil aviation that may endanger safety.

A separate 1971 Montreal treaty to which Belarus is also a party outlaws the seizure of aircraft or knowingly communicating false information in a way that endangers aircraft safety.