Hundreds braved the rain in the northwest English city for a silent vigil at 2131 GMT amid floral tributes, candles and teddy bears to honour the victims, who included six children.

As the number of people detained in Britain rose to 14, following an arrest early Monday morning, police also released new CCTV images of 22-year-old attacker Salman Abedi carrying a large suitcase and appealed for information about the luggage.

Abedi detonated his bomb just after the end of a concert by US pop star Ariana Grande in one of Europe's biggest indoor arenas in central Manchester. Many of the victims were either young concert-goers or parents waiting to take their children home.

A total of 116 people were injured in the attack, by Manchester-born Abedi, a university dropout of Libyan origin, 19 of whom remain in critical condition.

The Islamic State jihadist group has claimed responsibility for the attack.

"You tried to destroy us but you've brought us closer together," read one message of defiance left among the tributes in central Manchester, which included heart-shaped balloons and runners' bibs left by participants in a half-marathon on Sunday.

- Blue suitcase -

Investigators meanwhile pushed ahead with their probe.

Police could be seen conducting a search at a rubbish tip near Manchester and they released images of Abedi carrying a blue suitcase hours before the attack, asking the public where and when they might have seen him with it in the preceding days.

"We have no reason to believe the case and its contents contain anything dangerous, but would ask people to be cautious," the police said in a statement, stressing that the suitcase was different from the backpack Abedi used in the attack.

Abedi is believed to have returned from a trip to Libya a few days before the bombing and had also recently transited through airports in Istanbul and Dusseldorf in Germany.

The latest person held was a 23-year-old man arrested in the southern coastal town of Shoreham-by-Sea, more than 400 kilometres (250 miles) from Manchester.

Fourteen men are now detained on UK soil in the investigation, while Abedi's father and brother have been held in Libya, where officials said the two brothers were IS jihadists.

None of the men arrested in Britain have so far been charged with any crime and police have up to 14 days in which to do so under special anti-terrorism laws.

- M15 probe is 'right' -

Amid mounting criticism of the security services, the domestic intelligence agency MI5 is looking at decisions taken in the case of Abedi, who used to be on a terror watchlist but was no longer on it at the time of the attack, and whether warnings about his behaviour were ignored. 

"There is a lot of information coming out at the moment about what happened, how this occurred, what people might or might not have known," Britain's interior minister Amber Rudd told Sky News.

"It is right that MI5 take a look to find out what the facts are," she added.

British media have reported that two people who knew Abedi made separate calls to an anti-terrorism hotline to warn the police about his extremist views.

The Mail on Sunday also cited a source saying that US federal agents had been investigating Abedi since mid-2016 and had flagged up concerns to MI5.

The BBC reported that Abedi had taken part in the armed uprising against Libyan dictator Moamer Kadhafi's regime as a teenager during school holidays.

- Station reopening -

Britain's Prime Minister Theresa May on Saturday lowered the terror threat level, which had been hiked in the immediate aftermath of Monday's attack.

Operation Temperer, which involved the highly unusual deployment of armed troops on Britain's streets, was also being wound down on Monday night.

Cuts in police force numbers made while May was interior minister have become a focus for the campaign ahead of a general election on June 8 and polls have shown her ruling Conservatives' strong lead over the opposition Labour Party shrinking in recent days.

From 2009 to 2016, the number of police officers fell by almost 20,000, or around 14 percent.

May argues that the government has increased funding for security and intelligence agencies.

"What we had to do when we came into government in 2010 was to ensure that we were living within our means," May said when pressed about the cuts by a police officer during a televised question and answer session on Monday. (**)