The suicide bomber who killed 22 people in Manchester passed through Istanbul on his way to Europe but there were no records of him entering Syria during his travels, Turkish security officials told Reuters on Thursday.

They said Turkey received no warning from European countries about the bomber, Salman Abedi, so he was allowed to travel on to Europe.

Describing Abedi's movements before the attack, one official said: "There is flight traffic before his arrival to Europe. He travels first to Europe, then to a third country and then to Istanbul and back to Europe." He said the "third country" was not Syria.

"He has not spent any time in Turkey and he has not had an entry or exit from Syria during his travels, there is no such information in his records," the official said.

German intelligence official also told the Financial Times that Abedi flew from Istanbul to the UK via Dusseldorf’s international airport. Turkey’s government on Wednesday furnished British authorities with a file on Abedi, a senior Turkish official said.

Turkey has regularly been used as a transit point for European militants traveling to fight with ISIS in Syria’s civil war. However, it remains unclear whether Abedi spent time in Syria ahead of the bombing.

While eight people have been arrested in connection with the suicide bomb attack, university dropout Abedi's father Ramadan and younger brother Hashem were detained in Libya, authorities there said. Abedi's brother Hashem had been "under surveillance for a month and a half" and "investigation teams supplied intelligence that he was planning a terrorist attack in the capital Tripoli", the Deterrence Force said on its Facebook page. According to a security official in Tripoli, Abedi's father was a member of the Libyan Islamic Fighting Group that emerged in the early 1990s and fought against Muammer Gaddafi's regime.

British officials said Abedi had been on the radar of the intelligence community before the massacre. "It's very clear that this is a network that we are investigating," Manchester police chief Ian Hopkins told reporters.

Britain's terror threat assessment has been hiked to "critical", the highest level, meaning an attack is considered imminent.