LONDON -- A local official and media reports in Britain said Monday that two suspects arrested over last week's London subway bombing are an 18-year-old refugee from Iraq and a 21-year old believed to be from Syria, both of whom were fostered by the same elderly British couple.

The 18-year-old was detained Saturday at the port of Dover. The 21-year-old was held later the same day in Hounslow, west London.

Police are searching three addresses, including the suburban home of Penelope and Ronald Jones, who have served as foster parents for more than 200 children.

Local council chief Ian Harvey says he believes the 18-year-old is an Iraqi orphan who moved to the U.K. when he was 15. He says the 21-year-old, named by British media as Yahya Faroukh, was also fostered by the Joneses.

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The manager of a fried chicken restaurant in West London told the BBC that Faroukh was his employee and that he watched as undercover police officers surrounded him and took him into custody after his shift on Saturday night.

Restaurant manager Suleman Sarwar told BBC News on Monday that Faroukh always seemed like a "normal" guy during his several months of employment. He described him as a Syrian "refugee," though Faroukh's immigration status remains unclear.

"At some point he took some time off because his father died in Egypt... He tried to go out to Egypt but they wouldn't allow him being a Syrian refugee," Sarwar said, adding that Faroukh came back to work after a mourning period.

British police have not confirmed the identity of either of the suspects in detention. The Metropolitan Police only identify suspects once they have been officially charged with a crime.

Both men remained in custody and were being questioned Monday as commuters headed back to work in the first morning rush hour since the attack.

Authorities have reduced the terror threat level from "critical" to "severe," indicating they view another attack as highly likely, but no longer imminent. Police have asked the traveling public to be vigilant and to expect to see an increase in armed police.

Meanwhile, closed-circuit television images, acquired by ITV News and broadcast Sunday, appeared to show a person walking with a Lidl shopping bag in the suburb of Sunbury before Friday morning's attack at Parsons Green station that injured 30 people in southwest London. Images posted on social media following the attack appeared to show wires protruding from a flaming bucket contained in a Lidl bag on the floor of the train carriage.

The bomb only partially exploded. Officials say the injuries would have been far worse if it had fully detonated.

The 18-year-old suspect was arrested in the ferry departure area in the port of Dover on the English Channel. The other was arrested in west London. Both are being held under the Terrorism Act.

Police have searched several properties, including a home in Sunbury where an elderly couple served as foster parents for many children over several decades. They have been honored by Queen Elizabeth II for their work on behalf of children.

They have recently helped refugees from conflict zones including Syria and Iraq.

Most of the injured in Friday's explosion aboard a District Line train suffered flash burns while some were injured in the panicked rush to leave the Parsons Green station where the blast occurred.

The Islamic State of Iraq and Syria (ISIS) has claimed responsibility for the attack, but British officials say there is no proof yet that it was involved.