Police have confirmed they are investigating a "network" in connection with the Manchester bombing as it emerged an off-duty female officer was killed in the atrocity.

As a huge inquiry into the attack continued, the father of perpetrator Salman Abedi claimed his son was innocent, saying: "We don't believe in killing innocents. This is not us."

Ramadan Abedi said he spoke to his 22-year-old son Salman Abedi five days ago and he was getting ready to visit Saudi Arabia and sounded "normal".

He said that his son visited Libya a month and a half ago.

The elder Abedi told The Associated Press by telephone from Tripoli: "We don't believe in killing innocents. This is not us."

He said his other son, Ismail, was arrested in England on Tuesday morning.

He said Salman was planning to head from Saudi Arabia to Libya to spend the holy month of Ramadan with family.

Mr Abedi fled Tripoli in 1993 after Muammar Gaddafi's security authorities issued an arrest warrant and eventually sought political asylum in Britain.

Now, he is the administrative manager of the Central Security force in Tripoli.

In other developments on Wednesday detectives made a further three arrests in connection with the investigation, taking the number of people in custody to four.

Twenty-two people were killed and dozens more seriously injured when Abedi, 22, detonated a device as fans left Manchester Arena, where US star Ariana Grande was performing on Monday night.

Greater Manchester Police Chief Constable Ian Hopkins said the level of activity in the probe is "intense" and continuing "at pace".

Asked if officers are looking for the person who made the bomb, he said: "I think it's very clear that this is a network that we are investigating and as I've said, it continues at pace, this extensive investigation is going on and activity taking place across Greater Manchester as we speak."

Mr Hopkins confirmed that one of the victims of the attack was a serving police officer but provided no further details.

The BBC reported that the policewoman's husband is critically ill and her two children were injured.

Sources said the family are from Cheshire.