London (CNN) Anti-terror police in the UK are continuing to question suspects recently arrested on suspicion of attempting to blow up a London Underground train.

An 18-year-old man and a 21-year-old were arrested separately by police on Saturday, a day after the incident, according to UK police.

Police announced Tuesday the arrest of a 25-year-old man in Wales. There also were searches at four addresses, Metropolitan Police said.

The first two men arrested had been fostered by the same elderly couple, and at least one was a refugee from Iraq, local officials told CNN on Monday.

The 18-year-old was arrested by police in the departure lounge of Dover ferry port, which is the busiest ferry hub in Europe and a gateway to the French coast, police said.

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