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KATHMANDU, Dec 22 (Reuters) - The United Nations and the United States criticised on Monday a weekend attack by activists on a Nepali publishing house in which witnesses said journalists were beaten and the office ransacked.

About 50 activists, self-described supporters of Nepal's ruling Maoist party, went to the office of Himalmedia, publishers of the weekly English-language Nepali Times and other magazines, and broke windowpanes before beating staff on Sunday.

The activists said they were angry at critical coverage.

"This is a direct attack on free press and democracy," said Kunda Dixit, editor of the weekly.

Some staff received minor injuries, he said.

About 300 journalists and human rights activists marched through Kathmandu on Monday to protest against the attack.

Six people were injured when riot police used batons to break up the protest rally, said Jagat Nepal, a member of the Federation of Nepalese Journalists.

The Maoists abandoned a decade-long civil war two years ago and lead a coalition government after emerging as the biggest political party in an April election.

But they are being criticised by rival political parties for continuing violence and intimidation despite joining the political mainstream.

The United States and the Nepal office of the U.N. human rights agency condemned the attack and urged authorities to investigate the incident.

"There is no justification for the use of violence and intimidation by any party or organisation in an attempt to control the media or threaten freedom of the press in Nepal," the U.S. embassy said in a statement.

The Maoist party, which has vowed to protect press freedom, said it would investigate. (Reporting by Gopal Sharma; Editing by Bappa Majumdar and Dean Yates)

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