Pakistan has extradited to Norway a known extremist suspected of masterminding an Oslo shooting on the eve of the 2022 Pride festival, Norwegian authorities said on Friday.

On the night of June 25, 2022, just hours before the Pride parade was to take place, a man opened fire outside two bars in central Oslo, including a well-known gay club, killing two men and wounding nine others.

The suspected shooter, Zaniar Matapour, a 44-year-old Norwegian of Iranian origin, is currently on trial accused of an "act of terror".

Matapour has pleaded not guilty, and psychiatric experts are at odds over his mental health and thereby his legal responsibility.

Arfan Bhatti, a 46-year-old suspect who has lived and is well known in Norway, is suspected of having planned the attack but left Norway for Pakistan before the shooting.

Even though Norway and Pakistan have no agreement on extraditions, Pakistani authorities agreed to grant Oslo's request.

"Arfan Bhatti is now on a plane escorted by Norwegian police," Norway's Justice Minister Emilie Enger Mehl told reporters on Friday.

Bhatti, who denies any involvement and had opposed extradition, will be placed in custody on arrival in Oslo, Norwegian police said.

He is suspected of being an "accomplice to an aggravated act of terror", a charge that carries a prison sentence of up to 30 years.

Bhatti is expected to be called to testify during Matapour's trial, police said.

Bhatti's lawyer was angry that his client was extradited before Pakistan's supreme court had a chance to rule on his case.

"This way of doing things calls into question the respect of law and international legal principles," John Christian Elden said.