Hashem Abedi, the younger brother of suspected Manchester Arena bomber Salman Abedi, has been arrested in Libya on suspicion of having links to Isis.
Reuters reports that counter-terrorism police arrested Hashem in the country's capital, Tripoli.
The Abedis were born in Manchester to refugee parents, believed to have fled Libya to escape the Gaddafi regime.
A 23-year-old man, thought to be the other brother of the attacker, has already been arrested by Greater Manchester Police.
Four other men – three in south Manchester and one in Wigan – have also been arrested by British police in connection with the Manchester suicide bomb attack
Greater Manchester Police Chief Constable Ian Hopkins added it is "very clear" that police are investigating "a network" linked to Abedi and are seeking his possible accomplices.
Police used an explosive device to gain entry into flat in Manchester city centre as part of the investigation into the attack. The atrocity left 22 men, women and children dead.
Elsewhere, the father of the suspected attacker denies his son is linked to Isis or responsible for the blast.
Speaking to the Associated Press, Ramadan Abedi said he spoke to his son five days ago as he was getting ready to visit Saudi Arabia and sounded "normal". The father added: "We don't believe in killing innocents. This is not us."
French interior minister Gerard Collomb believed Abedi travelled to Syria from Libya and had "proven" links with Isis.
He told BFMTV: "Today we only know what British investigators have told us – someone of British nationality, of Libyan origin, who suddenly after a trip to Libya, then probably to Syria, becomes radicalised and decides to carry out this attack."