The government is tightening up vetting of American families and organisations hosting international exchange students amid a spate of recent abuse cases, some involving teachers.

New proposals expected to be formally adopted in October, call for adult hosts to be checked against sex offender registers and for organisers of foreign exchange programmes to undergo criminal background checks.

On students’ arrival in America, organisers will also be expected to inform them how to identify and report inappropriate behaviour. “We decided it was necessary to build an extra level of protection,” a US State Department spokesman said.

A Washington DC-area biology teacher is to be sentenced this month after admitting entering the bedroom of a 17-year-old German student staying at his home at 2.30am and pestering her for oral sex, having previously fondled her and walked round the house naked.

Also this month, a Michigan man will be sentenced for secretly videotaping a 16-year-old German girl in his care in various states of undress, local police said.

Last year, a California teacher received a three-year jail term for having sex with a 15-year-old German girl staying with him.

The State Department, said it has recorded five sexual assaults of international students by hosts in the past decade. Annually, about 28,000 international students stay with US families and attend local schools on visits brokered by privately-run agencies.

John Hishmeh, executive director of the Council on Standards for International Educational Travel, the industry’s accreditation body, said few agencies run background checks on hosts.

He welcomed the proposed screening measures but expressed concerns about the cost and time involved. “If you’re running a programme for 2,000 kids, that’s 4,000 parents, so they’ll have a broad impact.”

Mr Hishmeh said local agency representatives, appointed to oversee student placements, are a vital defence against abuse.

But in Arkansas, a local co-ordinator and ex-host for ERDT SHARE!, a California-based agency that brings 750 students to America each year, is awaiting trial on rape and sexual assault charges involving three 16 to 17-year-old male students.

Officials of ERDTSHARE! had previously stripped Doyle Meyer of host duties after an internal inquiry revealed he had massaged students, may have discussed sex with them, and gave them cigarettes and alcohol. But they allowed him to remain as local co-ordinator - overseeing 14 to 15 students - and did not involve police. They said they were shocked by subsequent allegations that Meyer had molested students.

Mr Hishmeh said Meyer should have been dismissed and police alerted but added that the proposed vetting would not have stopped the alleged abuse and other recent incidents because none of the suspects or perpetrators had previous convictions.