The raids come as experts are increasingly certain that killer Salman Abedi (pictured above) acted as part of a larger terror network which helped him carry out his attack.
The counter-terrorism force detained the father, Ramadan Abedi, outside his home in the Tripoli suburb of Ayn Zara on Wednesday afternoon.
The city of Manchester is expected to hold a moment of silence in tribute Thursday.
Abedi, who was born in Manchester in 1994 to Libyan parents, blew himself up on Monday night at the Manchester Arena indoor venue at the end of a concert by USA pop singer Ariana Grande attended by thousands of children and teenagers.
"It's like your own family just passed away, it's just so, so sad", 69-year-old Carmel McLaughlan told AFP, standing next to the sea of flowers filling the square.
"It's awful. Very wicked, to target that sort of thing", the 91-year-old monarch told 14-year-old Evie Mills and her parents. It also said Hashim was in Manchester during the planning for the attack and that he had been aware of the plot.
Twelve of the injured are under 16.
"We're strong but mighty", said resident Sophia Goodman.
British Prime Minister Theresa May said she plans to discuss the leaks with President Donald Trump at the North Atlantic Treaty Organisation summit in Brussels. Her French counterpart Gerard Collomb said the man had links with Islamic State and had probably visited Syria as well. US President Donald Trump has threatened to prosecute those responsible for the "deeply troubling" security breach.
After Manchester Arena attack, Ariana Grande suspends world tour till 5 June
The woman was arrested after armed police raided a block of flats in the north of Manchester , Sky News reported on Wednesday . This has made the total number of suspects linked to the attack rise to seven so far, Xinhua news agency reported.
Photographs of the bomb scene - controversially published by the New York Times against the wishes of counter-terror police - appear to indicate an elaborate explosive device engineered for maximum carnage.
"Until the operation is complete, we can't be entirely sure that it is closed". Libyan media and bloggers reported alleged connections between Abedi and the Libyan Islamic Fighting Group (LIFG), a militant Islamist organisation formed by Libyans who travelled to Afghanistan in the 1980s to fight Soviet troops and later plotted to topple former Libyan leader Muammar Gaddafi.
Eight suspects are now in detention on United Kingdom soil in connection with the blast, for which the Islamic State group has claimed responsibility.
German police said Abedi made a brief stopover at Duesseldorf Airport, while a Turkish official said he had transited through Istanbul airport without saying where he was travelling from.
"I want to make one thing very clear to Jeremy Corbyn and to you, and it is that there can never, ever be an excuse for terrorism", May said.
A British official said that Abedi had been on the periphery of the intelligence radar before the massacre. Eight suspects are now in custody. A woman detained on Wednesday was released without charge.
Prime Minister Theresa May said the independent body which sets the threat level had decided it should be lowered from its highest rating "critical", which meant an attack could be imminent, to "severe". The move will see the Army deployed to secure key sites.
Police said on Saturday that overnight they had made two further arrests as they closed in on other possible cell members.
The attack was the deadliest in Britain since 2005 when four extremist suicide bombers attacked London's transport system, killing 52 people.