Manchester police make 2 more arrests in connection with concert terror attack

British police made two more arrests early Saturday in connection to Monday's terror attack at a crowded concert hall in Manchester that killed 22 people.

Officers executed a search warrant and used a controlled explosion to gain entry to an address where two men -- ages 22 and 20 -- were arrested.

A total of 13 people have been arrested in the terror investigation, two of whom have been released without charge, the Greater Manchester Police said.

Eleven people remain in custody in connection with Monday night's suicide bombing at Manchester Arena, where American singer Ariana Grande had just finished performing.

The ages of the detained men range from 18 to 38, police said.

On Friday, the police said that a man was arrested in Moss Side, an impoverished neighborhood nestled south of Manchester city center.

The Friday evening arrest targeted a 44-year-old man in the Rusholme area who was taken into custody on suspicions related to the attack.

Authorities have said that Salman Abedi, the 22-year-old suspected suicide bomber who died in the explosion, grew up in an area near Moss Side.

There are 12 locations police are continuing to search and police activity will continue throughout the weekend, according to Greater Manchester Police Chief Constable Ian Hopkins. Manchester Arena is still cordoned off.

Britain's top counter-terrorism police officer, Assistant Commissioner Mark Rowley, said in a statement that police have made "significant arrests and finds" in the investigation, adding that they had gotten "hold of a large part" of Abedi's network.

"We are focusing on understanding Abedi's life; forensically examining a number of scenes, reviewing hours of CCTV from the night itself and the hours and before, financial work, communication, digital exhibits, the accounts from hundreds of witnesses and of course enquiries internationally," Rowley said.

Rowley said "immense" progress has been made and that more arrests are likely.

"It has been a challenging week and we are still in the middle of a live investigation," Hopkins said in a statement Friday. "We have hundreds of officers that are working on this investigation from across the national counterterrorism policing network and we have seized thousands of exhibits that are now being assessed."

Hopkins urged the public to "remain vigilant in the coming days" as the "threat level is still at critical."

A senior security source told BBC News that the threat level was raised to critical partly because of concern about the possibility of copy-cat attacks.

Manchester police said they have seen an increase in reports of hate incidents this week, from 28 on Monday, which Hopkins said is what they receive on an average day, to 56 on Wednesday.

"We can't directly link these to the events of Monday night and are continuing to monitor the situation," he said.

In addition to those killed, 116 people have been treated for injuries from Monday's attack and 75 were hospitalized, including 23 patients who are currently in critical care, according to the National Health Service (NHS) in England.

ABC News' Julia Jacobo, Rachel Katz, Kirit Radia and Joseph Simonetti contributed to this report.