LONDON (AP) UPDATE: Manchester police say the man who set off an improvised explosive device at an Ariana Grande concert in northern England died in the attack.
Police said Tuesday 22 people died in the attack Monday night. It wasn't clear if that included the suspected suicide bomber. Dozens more were injured.
Chief Constable Ian Hopkins said forensic investigations are continuing as police try to determine if the attacker had accomplices.
He did not provide any information about the individual who detonated the device.
The Latest on the blast at an Ariana Grande concert in northern England (all times local):
Greater Manchester Police say they have arrested a 23-year-old man in connection with the apparent suicide bombing at an Ariana Grande concert in the city.
Police say the man was arrested in south Manchester Tuesday, a day after the explosion killed 22 people and injured 59, many of them teenagers.
They did not provide details.
Police also said officials arrested a man at the Arndale shopping center in central Manchester - but that the arrest is not believed to be connected to Monday night's attack.
Italian Premier Paolo Gentiloni says efforts are underway so that this week's G-7 summit in Sicily will yield a stronger, common anti-terrorism commitment.
Condemning the bombing that killed 22 people in Manchester, England, Gentiloni told reporters Tuesday in Rome that the summit on Friday and Saturday provides the opportunity to insist that "the cowardliness that snuffs out the lives of young people won't get the better of our freedom."
He said Italians can count on the "dedication and professionalism" of their nation's security forces to ensure international events are carried out safely.
He says he planned to call British Prime Minister Theresa May to express "closeness, solidarity" to Britons.
Police have evacuated a large shopping center in Manchester, England. Police declined to comment on media reports that they have arrested a man there.
July McKenzie, who was shopping when the Arndale shopping center, said: "We were just in the shop and could hear people screaming and security guards telling everybody to get out."
Some people left the scene in tears, while others waited outside the mall.
The Arndale center was rebuilt after an IRA bombing in 1996.
Turkish officials say they "strongly condemn" the attack in Manchester and promised to work together with the United Kingdom against terror. President Recep Tayyip Erdogan says that Turkey "shares the pain of the state of England and the English people" in the attack that killed 22 people.
Turkey has been hit by a string of attacks blamed on the Islamic State group and Kurdish militants since 2015, killing at least 550 people.
British Prime Minister Theresa May says that it is "beyond doubt" that Britain and the city of Manchester have fallen victim to "a callous terrorist attack."
Speaking outside her offices in London, she says "Although it is not the first time Manchester has suffered in this way, it is the worst attack the city has experienced, and the worst ever to hit the north of England."
May says police believe they know the attacker's identity but are not disclosing it immediately.
British Prime Minister Theresa May says police and security staff in Manchester believe they know identity of the apparent suicide bomber who attacked people leaving an Ariana Grande concert Monday night, but they are not revealing the name for the time being.
Speaking in London, May said: "This attack stands out for its appalling, sickening cowardice."
She says the attack, in which 22 people died, was one of the worst the nation had suffered.
Harun Khan, the secretary general of the Muslim Council of Britain, has joined the condemnations of the Manchester attack.
In a statement, Khan says: "This is horrific, this is criminal. May the perpetrators face the full weight of justice both in this life and the next."
He adds: "I urge all those in the region and around the country to pool together to support those affected."
Finance ministers from the 28 European Union countries, including Britain's Philip Hammond, observed a minute's silence in memory of those killed and injured in the attack at an Ariana Grande concert in Manchester.
Ahead of the regular EU meeting of finance ministers, Hammond expressed his condolences to the victims and their families of "this barbaric attack" in Manchester.
"It is, as far as we know, a terrorist incident," he said. "We are treating it as such."
Hammond, who was due to speak at a panel in Brussels, is to return to London at the meeting's conclusion instead.
Flags are also flying at half-staff outside the European Commission in the heart of the Belgian capital.
France's interior minister says the government will be issuing instructions Tuesday to regional administrators on working with event organizers on how to secure public spaces.
After a high-level security meeting in Paris Tuesday, Interior Minister Gerard Collomb said organizers of sports events, concerts and other performances already had a series of instructions on how to secure their venues. Collomb said France's airports have also been secured.
France has been on heightened alert since the Nov. 13, 2015, attacks that struck a concert, the national stadium and cafes and bars.
Early Tuesday, the Paris mayor's office said all shows and concerts scheduled in coming days are going ahead as planned. Ariana Grande is scheduled to perform in Paris on June 7.
Police say 19 people have been confirmed dead with around 50 others injured following reports of an explosion Monday night at an Ariana Grande concert in Manchester, England. A representative said the singer was not injured.
There were no immediate details of what happened during the concert by the American singer at Manchester Arena, but witnesses reported hearing two loud bangs coming from near the arena's bars.
One U.S. law enforcement source says there was one, possibly two explosions inside the arena. Law enforcement officials are looking at the incident as terrorism, CBS senior investigative producer Len Tepper reports.
Joseph Carozza, a representative from Grande's U.S. record label, said the singer is OK and they are investigating what happened.
"A huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena," concertgoer Majid Khan, 22, told Britain's Press Association. "It was one bang and essentially everyone from the other side of the arena where the bang was heard from suddenly came running towards us as they were trying to exit."
Added Oliver Jones, 17: "The bang echoed around the foyer of the arena and people started to run."
Police advised the public to avoid the area around the Manchester Arena, and the train station near the arena, Victoria Station, was evacuated and all trains canceled.
"Due to an incident involving the emergency services [Manchester Victoria] has been evacuated," Northern train service officials said. "We will provide further updates when possible."