Tunisia arrests nephew of Berlin suspect

The nephew of the suspected Berlin truck attacker and two other alleged militants "connected" to the assailant Anis Amri, were arrested by Tunisian authorities, the interior ministry said on Saturday.

A statement said that the three suspects were members of a "terrorist cell... connected to the terrorist Anis Amri who carried out the terrorist attack in Berlin".

The suspects were arrested on Friday, as reports emerged suggesting the main suspect in the Berlin Christmas market attack officially pledged allegiance to the Islamic State group.

In a video released by IS-linked agency Amaq, Tunisian Anis Amri, who was killed when he opened fire on Italian police on Friday, pledged allegiance to IS self-described "caliph" Abu Bakr al-Baghdadi.

"I vow to obey the caliph Abu Bakr al-Baghdadi in whatever he orders me to do even if it is to my disliking," Amri said.

The two-minute, 42-second video showed Amri speaking directly to a camera while standing outdoors wearing a winter coat and earphones.

It was unclear when the video was filmed. It appeared to have been shot in Berlin.

As well as his pledge of allegiance, Amri declared his desire to avenge Muslims killed in air raids and called for attacks against "crusaders".