The two men arrested by British police were detained after Italian police requested their extradition on terrorism charges.
Ali Ben Zidane Chehidi, aged 34, was arrested in Croydon, southeast England and Mohamed Salah Ben Hamadi Khemiri, aged 53, was arrested in Manchester, northwest England.
"The two men were arrested on behalf of the Italian authorities under an extradition warrant in relation to allegations that between 2003 and 2005 they forged documents to facilitate the illegal entry into Italy of recruited volunteers to fight jihad in Iraq and Afghanistan," British police said in a statement.
A French police source told the Reuters news agency that the DST domestic intelligence service had been involved in a broader European operation linked to the arrests in Italy.
A number of suspects were detained but no further details were immediately available, the source said.
The operation was ordered by prosecutors in Milan.
The suspects were also accused of illegal immigration, falsifying identity documents and helping to hide people sought for terrorist activity, the police said.