Police have arrested a Kenyan suspected of aiding the armed men who kidnapped a British tourist and killed her husband on the remote island resort of Kiwayu island, near the border with Somalia, according to an official.

David and Judith Tebbutt had arrived at the Kenyan resort during the day on Saturday and were attacked in their room shortly after midnight.

Stephen Ikua, the government administrator of Kenya's Lamu West district, said on Tuesday that a suspect in custody was believed to have information about the organiser of Judith Tebbutt's kidnapping and her husband's killing.

He said the organiser was a Kenyan who operated in Somalia and had links to the armed Somali group al-Shabab.

Al-Shabab, which aims to topple Somalia's government, has threatened to attack Kenya on several occasions.

Ikua said he thought the group may have fled to Somalia with Tebbutt, but he was not aware of any communications with the kidnappers.

He declined to give further details, citing ongoing investigations.

'Doing everything possible'

London's Metropolitan Police said on Tuesday some of its officers were working with Kenyan authorities.

London police said the force had sent a "small team" to Kenya but declined to say how many officers were in the country. They said that Kenyan authorities remained the lead investigators.

Armed security officers patrolled the resort on Monday, with guards posted on the white-sand beach, fringed by palm trees.

A massive manhunt for the woman's abductors has been beefed up by police search boats and helicopters, according to an AFP reporter travelling on a boat through the area.

"Our forces have been out since Sunday doing everything possible to rescue her," Aggrey Adoli, the regional police commander leading the search, said.

"We have also appealed to members of the public in this area to work closely with us."

Kiwayu island and the surrounding area is one of Kenya's top luxury holiday destinations and favoured by celebrities, despite being close to the border with war-torn and drought-struck Somalia.