Police investigating failed July 21 bomb attacks in London said Monday they had arrested two men during raids in the city, as authorities tried to determine whether there were links between that attack and the transit bombings two weeks earlier.

A total of 23 people have been arrested in connection with the failed bombing attempt, including the four main bombing suspects in police custody in London and Rome.

The July 21 bombing came exactly two weeks after July 7 attacks that killed 52 people plus all four suicide bombers. Both attacks both hit three subway cars and a red double-decker bus, but the July 21 attackers’ explosives failed to detonate and took no lives.

The men in the arrests announced Monday have been detained “on suspicion of the commission, preparation or instigation of acts of terrorism,” a Metropolitan Police spokeswoman said. They were arrested after searches of three properties in the Stockwell and Clapham areas of south London.