LONDON — Police detained a new suspect yesterday in the alleged plot to blow up jetliners over the Atlantic — the first arrest since authorities detained two dozen people last week and threw Britain’s airports into turmoil by imposing tougher security.

The announcement came after police said they raided two Internet cafes near the homes of some suspects, and a news report said officers might have found a rifle and a pistol in a search of woodlands in the same area.

Travelers still faced problems at Britain’s main airports, where flight delays and cancellations exacerbated confusion over shifting rules on hand luggage.

London’s Metropolitan police said the latest suspect was detained around noon in the Thames Valley area, west of London. They did not disclose the person’s identity.

“A suspect has been arrested in connection with the investigation and is in custody in the Thames Valley area,” a spokeswoman said, speaking on condition of anonymity to comply with department rules.

The developments came after several days of near silence from British officials.Authorities will have to provide at least some details of their evidence when a judge holds a closed-door hearing today to decide whether to extend detention for 23 suspects. One suspect was released without charge Friday.

The two Internet cafes were raided Thursday in Slough, 25 miles west of London and not far from High Wycombe, where several suspects were arrested, Thames Valley police said.

A co-owner of the One World Internet Cafe, Nargis Janjua, said officers arrived Thursday afternoon and removed 25 computers from her shop and loaded them into a van.

“They told us they were watching for days and weeks before,” she said, adding that she had no idea why police were suspicious of activities in the shop.

The British Broadcasting Corp. reported that a search of woods in High Wycombe turned up firearms and other items of interest. It was not clear if they were tied to the alleged plot.

Investigations are also under way in Pakistan, where officials are holding 17 people, including a British citizen, Rashid Rauf, who they said has Al Qaeda connections and was a key player in the plot. At least one of Mr. Rauf’s brothers was arrested in England.

Pakistan’s Foreign Ministry said the country might extradite Mr. Rauf to Britain but had not yet been asked. An official in Britain’s Home Office said Mr. Rauf could come home within days and that further requests to extradite other British nationals would likely arrive in coming days. At least one other British citizen is being held in Pakistan, officials in Islamabad have said.

Security rules were eased at London’s airports. Passengers were allowed a single, briefcase-size bag as a carry-on and were also permitted to have cell phones, laptops, and other electronic devices. Cosmetics, gels, toothpaste, liquids, and sharp objects remained forbidden.

A British newspaper reported officials were considering a system of passenger profiling that would select people behaving suspiciously, having an unusual travel pattern, or being of certain ethnic or religious backgrounds.

Leaders in the Islamic community criticized the latter idea, saying it would further isolate British Muslims.

“There is concern that such profiling would perhaps only contribute to further alienating a group whose close cooperation is essential in countering terror,” Inayat Bunglawala of the Muslim Council of Britain said.