The ACLU says the Silver Ring Thing programme violates the principle that the state budget cannot be used to promote religion.

The programme, which targets teenagers, is an offshoot of a Christian ministry. Since 2003, it has received more than $1m from the Department of Health and Human Services.

Symbolic ring

The funding is part of a government initiative to expand abstinence-only sex education.

Although many government grant recipients have religious affiliations, they are not supposed to use the federal money for religious proselytising.

The lawsuit, filed in federal court in Boston, alleges that the Silver Ring Thing uses grant money to encourage young people to commit themselves to Jesus Christ.

"The courts have repeatedly said taxpayer dollars cannot be used to promote religion," said Julie Sternberg, an attorney with the ACLU's Reproductive Freedom Project.

"The Silver Ring Thing blatantly violates this principle."

Adherents to the programme wear a silver ring as a sign of their commitment to refrain from having sex until marriage.

The ACLU has complained that the programme's official rings are inscribed with verses from the Bible, 1 Thessalonians 4, 3-4, reading: "God wants you to be holy, so you should keep clear of all sexual sin. Then each of you will control your body and live in holiness and honour."

Chris Downing, a spokesman for the Department of Health and Human Services, told the Associated Press news agency that the department did not comment on pending litigation.

Denny Pattyn, the Silver Ring Thing's founder and president, issued a statement describing the programme as "faith-based", but said that the federal funds had been properly used at all times, the AP news agency reported.

The suit names only the Department of Health and Human Services officials, not the Silver Ring Thing, as defendants, and seeks to halt federal funding to the programme.

The Silver Ring Thing says more than 30,000 young people have committed themselves to premarital purity after attending the programme's three-hour presentations.