Two sex offenders on the run from Scotland's increasingly tight monitoring system were named yesterday.

Strathclyde Police said they were looking for two foreign nationals - Indian Surjit Singh and Malawian Frank Mvula - who are believed to have fled the country.

The force, which knows the whereabouts of all but five of its 1100 registered sex offenders, said the two men, both of whom were convicted of indecent assaults on women, had failed to comply with rules under which they must keep in contact with authorities after they leave jail.

Many of Scotland's two dozen or so missing sex offenders are believed to have escaped abroad, some to countries where there is no meaningful system for keeping a track on their movements.

Strathclyde yesterday said its tally of five missing men included Martin Cusick, a paedophile and former police officer whose photograph they published earlier this year. He has since made himself known to the force and is believed to be in Canada.

Detective Chief Superintendent Campbell Corrigan, Strathclyde Police's head of public protection, yesterday admitted detectives could not be absolutely sure Singh and Mvula were overseas but said extensive searches in the UK had failed to find them.

He said: "We would not like to hang our hat on exactly where they are or exactly what we think they are doing. We are being honest. But it is worthwhile publishing their pictures in the UK."

Authorities cannot be sure where Singh, who is 5ft 8in and balding, has been since he left jail in June 2005 after serving two months for a sexually aggravated assault against two 17-year-old women.

He is known to have been in England but a Glasgow address he gave to prison authorities turned out not to exist.

Strathclyde has been seeking Singh since May 2007, shortly after tougher and more effective Multi-agency Public Protection Arrangements or Mappa came into place.

There is no evidence that Singh has even been in Glasgow.

Mvula, who is 6ft 2in and speaks with a distinct African accent, was found to have disappeared in February 2006. He had been released from a three-and-half year prison sentence pending an appeal against his 2004 conviction for a serious indecent assault of a women in her 20s in Stirling.

Neither man has been assessed as being of a high risk of reoffending. Strathclyde officers have alerted colleagues in Africa and India, through "appropriate" international channels.

Police and their partners, including the Crown Office, rarely issue photographs of missing sex offenders.

Assistant Chief Constable Ruaraidh Nicolson said: "We have to strike a balance between considering public safety against the risk of prejudicing any future criminal proceedings and the risk to the offender himself.

"The impact on the general public and possibility of retribution against persons who may resemble the offender all require careful consideration and risk assessment before photographs are released into the public domain.

"The trauma suffered by victims of the offender is always uppermost in our mind when considering the release of offenders' details."

Police said they had still to decide whether to identify two other sex offenders "off the radar", aside from Singh, Mvula and Cusick.

The force recently reestablished contact with a missing sex offender, as a result of publicity surrounding the search for Cusick, whose picture was published despite his resemblance to his twin brother, also a former police officer.