LONDON (AP) — Two of the six men arrested over last week's London subway bombing were released without charge Thursday, British police said. Four others remained in custody.

One of those released is a 21-year-old, originally from Syria, detained outside a fast-food restaurant in west London on Saturday, a day after the rush hour attack on a subway train. The other is a 48-year-old man arrested Wednesday in Newport, Wales.

Thirty people were injured when a homemade bomb — placed inside a bucket wrapped in a supermarket bag — partly detonated on a train stopped at London's Parsons Green station.

The attack sparked a manhunt for the perpetrators and prompted officials to briefly raise the national terrorism threat to the highest level.

The suspects still being held include an 18-year-old from Iraq detained at the English Channel port of Dover on Saturday.

Two men aged 25 and 30 arrested in Newport earlier this week remained in custody, as did a 17-year-old detained early Thursday in south London.

None of the suspects has been charged, and their names haven't been released.