One person, Krekar's son-in-law, a 27-year-old British national, was lightly injured in the attack when a bullet hit him in the hand.

Krekar, 53, has lived in Norway for nearly 20 years. He and four other people were in the fourth-floor apartment when the attack occurred.

Investigators said they had no concrete leads yet.

"We don't know who is behind this attack nor the motive," Oslo police official Grethe Lien Metlid told reporters.

Just before the shots were fired from a nearby balcony, someone tried to break into the apartment.

"We've opened an inquiry into attempted murder," Metlid said.

Police said in a statement two people were seen leaving the scene after the shooting, "but it is too early to say whether they are linked to the incident."

Police were alerted to the attack at 01:54 am (0054 GMT), which took place in a working-class neighbourhood of eastern Oslo where Krekar has lived with his family since 1991.

"The whole family is shaken," Krekar's lawyer Brynjar Meling told television news station TV2 Nyhetskanalen.

"In the past, there were threats from nationalist circles that could be related to his activities in northern Iraq," he said.

Krekar, whose real name is Fateh Najmeddin Faraj, admits that he co-founded Ansar al-Islam in 2001 but insists he has not headed it since May 2002.

He and the group figure on United Nations and US lists of terrorist groups or individuals.

According to the former US administration of president George W. Bush, Ansar al-Islam served as a link between ex-Iraqi leader Saddam Hussein and Al-Qaeda, a disputed claim partly used to justify the US-led invasion of Iraq in 2003.

A neighbour of Krekar's told AFP he heard three shots fired at the apartment.

"Lots of police arrived quickly and took the entire family away under heavy security," he said.

Krekar has been living under risk of deportation since 2003 after Norwegian authorities ordered him expelled, claiming he posed a threat to national security.

While Norway's court system has upheld the ruling, Norwegian law however prevents him from being deported to Iraq, where he risks the death penalty.

Krekar has often supported the insurgency in Iraq, comparing the US occupation of the country to the Nazi occupation, and has also described Al-Qaeda chief Osama bin Laden as a "good Muslim."