Two women questioned under the Terrorism Act after their arrest at Manchester Airport have been released without charge. Two men, aged 48 and 27, also arrested at the airport on Monday, are still being questioned by Greater Manchester Police (GMP).
Meanwhile, GMP officers have raided a house in Hollyhock Road, Dudley - their second in West Midlands this week, BBC reports.
After the airport arrests, they raided an address in the town's Jasmine Road.
The arrests were made under section 15 of the Terrorism Act 2000, which involves "providing money or other property suspected of being used for the purpose of terrorism", according to This is London.
Following the arrests by armed police at Manchester Airport, officers raided a house in Dudley in the West Midlands.
A police spokeswoman said the arrests were not believed to have any link to terrorist activity in London.
So far, 15 people have been charged in connection with the failed attack on London's transport system on July 21. Four men have been charged with attempted murder and the fifth suspected bomber, Hussain Osman, is in custody in Rome, where he has been charged with aiding international terrorism.