Another former senior member of Portugal's Socialist Party is the latest ex-government official to be arrested in a corruption investigation that has seen a former prime minister held in prison.

The attorney general's office said Armando Vara, a deputy minister in two Socialist governments between 1995-99, was arrested on suspicion of corruption, tax fraud and money-laundering and would appear before an investigating magistrate Friday.

A statement said an arrest warrant for Vara was issued after searches of his home, a bank and business premises.

It said the suspicions against Vara, age 61, are part of the same case that brought the arrest last November of Jose Socrates, prime minister from 2005 to 2011. He has been held in prison since then while prosecutors build their case.