The assailant in last week’s attack on a synagogue in the British city of Manchester that left two congregants dead claimed allegiance to Islamic State group, police say.

The attacker, Jihad Al-Shamie, called emergency dispatchers during his deadly attack on October 2 to pledge his allegiance to the terror group, counter terrorism police said in a statement released on Wednesday (early Thursday AEDT).

Al-Shamie, 35, was shot dead by police outside the Heaton Park Congregation Synagogue in Manchester after he rammed a car into pedestrians, attacked them with a knife and tried to force his way into the building.

Congregation members Melvin Cravitz, 66, and Adrian Daulby, 53, died in the attack on Yom Kippur, the holiest day of the Jewish year.

Police say Daulby was accidentally shot by an armed officer as he and other congregants barricaded the synagogue to block Al-Shamie from entering. Three other men are hospitalised with serious injuries.

Police said that Al-Shamie was on bail over an alleged rape at the time of the attack, but hadn’t been charged.

As police have worked to determine whether or not the attacker acted alone, they have arrested three men and three women in the greater Manchester area on suspicion of the “commission, preparation and instigation of acts of terrorism”.

A court on Saturday granted police five more days to hold four of the suspects: men ages 30 and 32, and women ages 46 and 61.

An 18-year-old woman and a 43-year-old man were released with no further action, police said.

Police haven’t identified those arrested or disclosed their links to Al-Shamie.