Photo: Metropolitan Police

The two suspects detained over last week's London subway bombing are an 18-year-old refugee from Iraq and a 21-year old from Syria, both of whom were fostered by a British couple, according to a local official and media reports.

The 18-year-old was detained Saturday at the southeast England port of Dover, a departure point for ferries to France. The 21-year-old was held later the same day in Hounslow in west London. Photos published by the Sun newspaper showed a man being detained outside a fast-food restaurant in Hounslow, which was searched by police.

Both men are being held under the Terrorism Act and are being questioned at a London police station about Friday's attack. Neither has been charged.

Thirty people were injured when an improvised explosive device partly exploded aboard a crowded London Underground train at Parsons Green station during the morning rush hour. None of the injuries was life-threatening, and experts said it appears the main charge of the bomb didn't detonate.

After the rush-hour bombing, British officials raised the country's terror threat level to the highest level, "critical," meaning an attack may be imminent. They lowered it Sunday to "severe," and police said the investigation was making rapid progress.

Police searched three addresses, including the house in suburban Sunbury, outside London, of Penelope and Ronald Jones. The couple has been honoured by Queen Elizabeth II for fostering more than 200 children, including refugees from Middle Eastern conflicts.

Ian Harvey, who heads local Spelthorne Borough Council, said he believed the 18-year-old was an Iraqi orphan who moved to the U.K. when he was 15 after his parents died and had lived in the Sunbury house.

He said the 21-year-old was also a former foster child of the Joneses. Sky News and other British media named him as Yahyah Farroukh, who is originally from Syria.

West Thames College in West London said in a statement that "Yahyah Farroukh, who, according to media reports is the second suspect detained in connection with the Parsons Green incident, was a former student at the college from December 2013 to June 2015." 

Suleman Sarwar, co-owner of Aladdin's Fried Chicken in Hounslow, said Farroukh worked there and was arrested by police Saturday night at the end of his shift.

Stephen Griffiths, who lives across the street from Penelope and Ronald Jones, said police had visited the house several times, most recently two or three weeks ago.

"The police were there multiple times over the span of about a month — a few times a week," he said. "You always think foster kids are going to have a bit of trouble, but you don't think terrorism," he added.