The threats are reported to have involved Eastlake High School in a suburb of Seattle, Washington, which has about 1,240 students.

The local school district, Lake Washington, declined to give details of the threats or say how many people were involved.

In a statement, it said: "Over the weekend a serious threat in an internet chat room was made against students and staff at Eastlake High School.

"To protect the safety of students and staff, we have cancelled classes at Eastlake High School ... in the city of Sammamish, for Monday, November 1st.

"District staff will work with appropriate authorities in the investigation of the threat."

Meeting

A community meeting was to be held at Eastlake on Monday evening.

"I've got a feeling it's not going to take very long until we find out who's responsible," said John Urquhart, a spokesman for King County sheriff.

"Not only the school district, but we're going to come down on them like a ton of bricks because we don't like this happening," he said.

Extra security and metal detectors were in place for the reopening on Monday of a school where four boys were arrested last week on charges of planning a racially-motivated attack using bombs and guns.

The four, from South High School in Cleveland, Ohio, denied the charges on Sunday and were remanded in juvenile detention.