Police in Nigeria say they are no longer sure if an attack last week on police headquarters in Abuja was a suicide bombing.

Police said soon after the June 16 bombing that it was a suicide attack believed to have been carried out by the Islamist radical group Boko Haram.

The attack left at least two dead including the presumed suicide bomber and was believed to have been the first suicide attack in the country.

However, police issued a statement Wednesday saying they wanted to correct the record. The statement said the investigation has not been concluded as to whether the attack was a suicide bombing or not. Police officials took no questions and gave no further details.

A spokesman for Boko Haram claimed responsibility for the blast in an interview last week with VOA. The explosion outside Nigeria's national police headquarters in Abuja was so powerful that it destroyed more than 30 cars.

Authorities blame Boko Haram for a string of deadly attacks in Nigeria's north that have targeted police officers, government officials and other authority figures.

The group is pushing to impose strict Islamic law across the north.

It launched a brief uprising against the government in July 2009, sparking a heavy military response and a week of fighting that killed some 700 people.