Nine Mongolian environmentalists protesting against legal changes which they say will loosen controls on mining were arrested outside parliament on Monday after one fired a shot, reports and officials said.

Leaders of the Fire Nation NGO coalition, which includes some nationalistic organisations, attempted to enter the building where the Great Hural was to meet for a special session but were stopped by guards, and a gunshot was heard, police said.

Information portal news.mn said nine people were arrested and two guns confiscated including a Kalashnikov assault rifle. There was no immediate official confirmation of this.

"The demonstrators wanted to take a petition into the parliament house but were stopped by the guards. The demonstrators didn't shoot on purpose but fired a gun unintentionally," said police captain Yondon Lkhagvasuren, adding that no one was injured.

A mining boom has given sparsely-populated Mongolia one of the world's highest growth rates and created a wealthy new elite, but also raised accusations of exploitation and concerns over environmental consequences.

Ulan Bator brought in new foreign investment laws last year, since when incoming investment has fallen, and parliament was due to review the changes.

Fire Nation leader Tsetsegee Munkhbayar previously said that Mongolian laws delaying mining activities would be neutralised by the revised proposals, and the group had drawn up a text of its own.

"We will make them adopt this resolution," he said last week.

The Central Tower, a luxury shopping and office development in Ulan Bator was evacuated on Monday, employees said, while reports said there was a bomb threat at the environment ministry nearby. There was no official comment.