The promise of a period of silence in the classroom might be expected to be uncontroversial - but in Virginia in the United States it is re-opening arguments over the place of religion in schools.

The state has passed a law requiring every school to begin the day with a minute's silence, in which students can "meditate, pray or engage in other silent activity".

But the American Civil Liberties Union has begun legal action to oppose the measure, arguing that it is a back-door way of introducing public prayer in schools.

The civil rights organisation says the minute's silence, which is proposed for September, breaches the constitutional block on the promotion of religion by the state.

'Nod and a wink'

"It is an attempt to put state-sanctioned prayer back in our public schools, and that is both shameful and unconstitutional," said Kent Willis, the union's executive director in Virginia.

Even though the daily silence might appear to be an inoffensive measure, the ACLU says that it is an attempt to circumvent rules on prayer in school with "a nod and a wink".

The dispute over the minute's silence will be the latest in a series of law suits seeking to define the boundaries of religion within schools in the United States.

Earlier this month, the Supreme Court ruled against public prayer being allowed before school sports events.

And there have been a number of long-running disputes over whether the Ten Commandments can be displayed in classrooms or school sports grounds.