A Pakistani court has allowed federal investigators to hold an American for another three days to investigate how he re-entered Pakistan despite being barred from the country.

Investigator Rana Akram said Judge Naveed Iqbal on Tuesday granted investigators three more days to investigate Matthew Barrett.

Barrett was arrested in Islamabad this weekend.

The 33-year-old was first arrested in May 2011 near a secretive military research facility and was barred from returning to Pakistan. But he obtained a visa from the Pakistani consulate in Houston and managed to clear the airport immigration counter.

The interior minister has ordered an inquiry into how Barrett managed to enter Pakistan again and suspended the airport immigration staff for negligence.

Barrett had lived in Pakistan for four years, married a Pakistani and had two children.