Manchester – London, British authorities arrested eight suspects on Thursday in the investigation into Monday’s bombing at an Ariana Grande concert in the city of Manchester that left 22 people dead and 75 injured.

One suspect was arrested in the suburb of Wigan in the greater Manchester area, while another was detained in the center of the city.

A woman who was detained on Wednesday night was released without charge.

British authorities had arrested on Tuesday and Wednesday six men on suspicion of being involved in the attack. Libya meanwhile held the father and brother of Salman al-Abedi, the suspected suicide bomber who carried out Monday’s attack.

Abedi, 22, is a British national of Libyan descent.

He had expressed a desire to avenge the killing of a friend in the British city last year, a source close to his family said Thursday.

His friend, also of Libyan descent, died after being stabbed by British youths in Manchester in May 2016, the source said on condition of anonymity.

“That incident stirred up a sense of anger among young Libyans in Manchester and especially Salman, who clearly expressed his desire for revenge,” he said.

“I personally talked with him and tried to convince him that it was just a criminal act,” he added.

British media reported that Abdul Wahab Hafidah died after being run over and stabbed in the neck in Manchester’s Moss Side district in May last year.

His suspected killers are still on trial.

Manchester Chief Constable Ian Hopkins said Abedi had not acted alone, adding it was “very clear that this is a network that we are investigating.”

“I want to reassure people that the arrests that we have made are significant, and initial searches of premises have revealed items that we believe are very important to the investigation,” he added.

With the official threat level raised to “critical”, meaning a further attack could be imminent, troops have been deployed to free up police, and armed officers patrolled trains for the first time in Britain.

In the nearby town of Wigan, where a man was arrested on Wednesday, police said they had discovered potentially suspicious items, prompting them to bring in the bomb squad and evacuate properties in the area. The security alert was later lifted.

Meanwhile, US President Donald Trump said on Thursday that “deeply troubling” leaks to US media
about the Manchester suicide bombing would be investigated, after irate British police briefly stopped sharing information with US Agencies.

Prime Minister Theresa May raised British concerns with Trump at a NATO summit in Brussels, telling him intelligence shared between their two countries had to remain secure, in a rare public show of dissatisfaction with Britain’s closest security ally.

After a suspension that lasted about a day, Britain’s most senior counter terrorism officer said late on Thursday that the police had resumed sharing information with the United States after receiving “fresh assurances”.

Trump had called the leaks “deeply troubling”.

“I am asking the Department of Justice and other relevant agencies to launch a complete review of this matter, and if appropriate, the culprit should be prosecuted to the fullest extent of the law,” he said in a statement released after his arrival in Brussels.

Pictures published by the New York Times included remains of the bomb and of the rucksack carried by the suicide bomber, and showed blood stains amid the wreckage.

In a statement, the New York Times defended its decision to publish the images, saying they were “neither graphic nor disrespectful of victims”.

“Our coverage of Monday’s horrific attack has been both comprehensive and responsible,” the newspaper said.

US Secretary of State Rex Tillerson will make his first official visit to Britain on Friday in an expression of solidarity following a suicide bombing in Manchester earlier this week, the British government said.

During his visit Tillerson will meet British Foreign Secretary Boris Johnson in London.

“Secretary Tillerson and the Foreign Secretary will write messages of condolence for the victims of the attack and hold talks on a range of foreign policy issues,” the Foreign Office said in a statement.

British security services have thwarted 18 militant plots in the UK since 2013, including five following an attack in central London in March, a source with knowledge of the matter told Reuters.

“MI5 is managing around 500 active investigations, involving some 3,000 subjects of interest at any one time,” the source told Reuters on condition of anonymity.

MI5 is trying foil several plots against Britain at any one time, the source said, adding that the Manchester suicide bomber, Abedi, had been on its radar.

“Abedi was one of a larger pool of former subjects of interest whose risk remained subject to review by MI5 and its partners,” the source said.

“Where former subjects of interest show sufficient risk of re-engaging in terrorism, MI5 can consider re-opening the investigation, but this process inevitably relies on difficult professional judgments based on partial information.”