Kenya's foreign minister has told the BBC his country has sent troops into neighbouring Somalia to target the Islamist insurgent group al-Shabab. It follows the kidnapping last week of two Spanish aid workers employed by the medical charity Medecins Sans Frontieres (MSF) at the Dadaab refugee camp, 80km (50 miles) from the border with Somalia.
A British man and a Frenchwoman have also died during abductions in Kenya in recent weeks and a British woman remains missing - she is believed to be held by al-Shabab.
This is a summary of what is known about them.
Judith Tebbutt, 56, was on holiday with her husband David at the remote Kiwayu Safari Village resort when armed men burst into their cottage on 11 September. They had only arrived the previous day; they were the only guests at the resort.
The resort consists of simple thatched cottages dotted along the beach. The cottages have no solid doors, just cloth curtains hung across entrances.
Police told the BBC six gunmen had burst into the couple's room.
Mr Tebbutt was shot dead, while his wife was taken away in a speedboat, possibly by Somali pirates. Police commissioner Mathew Iteere speculated that David Tebbutt may have been shot because he was resisting the gunmen.
Mrs Tebbutt is believed to have been taken across the border into Somalia, about 45km (28 miles) from the resort.
The Tebbutts' home is in Bishop's Stortford, in Hertfordshire. Mrs Tebbutt, a social worker, is believed to be deaf and to wear a double hearing aid. Her husband worked in publishing and sat on the board of a book charity.
Two men have appeared in court in connection with the attack on the Tebbutts. Both have pleaded not guilty. One of them, Ali Babitu Kololo, told the court he was forced at gunpoint to lead a group of men to the hotel and was not a willing accomplice.
The Foreign Office continues to advise against all but essential travel to within 30km (18 miles) of Kenya's border with Somalia. There have been previous attacks by Somali militia into Kenya, it says.
Marie Dedieu, 66 years old and disabled, had been spending seven or eight months a year in Kenya since the mid-1990s.
In the late 1960s, she was seriously injured in a car accident and was confined to a wheelchair.
A journalist and feminist activist in France, she worked at a feminist magazine in the 1970s and campaigned for the liberalisation of abortion laws.
Initially, Mrs Dedieu lived on the island of Lamu, in the archipelago of the same name. Although Lamu derives up to 90% of its income from tourism, it is still off the beaten track.
Lamu Old Town has been declared a World Heritage Site by the UN cultural organisation Unesco, which describes it as "the oldest and best-preserved Swahili settlement in East Africa... built in coral stone and mangrove timber".
About seven years ago, Mrs Dedieu rented a patch of land on the island of Manda, opposite Lamu island. She built a small house there, in a traditional Swahili style, with a turf roof.
She called it her "little corner of paradise".
Residents of Lamu and Manda told the French newspaper Le Figaro that Mrs Dedieu was popular in the community, a familiar figure at weddings and local events.
"Frankly, she is an extraordinary woman and we are very sorry about what has happened, especially that it has happened to her," deputy mayor Ajar Ali told the paper.
In the early hours of 1 October, Mrs Dedieu was abducted by a gang of armed men. She had only returned three days earlier from a visit to France, arousing suspicions that her abduction had been planned with the help of local informants.
She was on medication, which she had to take every four hours. Her kidnappers did not take her wheelchair or medication with them.
The French foreign ministry has established that Mrs Dedieu was taken to the Somali coast. A Kenyan man was arrested on 3 October and questioned by local police but has since been released.
On 19 October, the French foreign ministry said it had heard from its contacts that Mrs Dedieu had died, saying that her poor health and lack of medication meant that "tragic outcome was unfortunately most likely".
Officials condemned the "total lack of humanity and the cruelty" shown by the kidnappers, and demanded they be brought to justice.
Montserrat Serra y Ridao, 40, was abducted from the Dadaab refugee camp in Kenya on 13 October, along with her colleague, Blanca Thiebaut. Their Kenyan driver, Mohamed Hassan Borle was injured in the attack and is recovering in hospital.
At the time of her abduction, Miss Serra had been in Kenya for two months. She was working as a logistician for MSF in Dadaab, the world's largest refugee camp. It houses around 450,000 people who have fled famine and conflict in the Horn of Africa, especially Somalia.
Miss Serra qualified as a teacher before taking a master's degree in co-operation and development. She was working as a teacher in the technology department of a secondary school in Girona but took a leave of absence to go to Kenya.
Before she came to Dadaab, Miss Serra had worked on aid projects in Latin America and Yemen.
MSF Spain says it has set up a crisis committee to handle the incident. However, it is releasing few details.
"Any publicity given to this incident does not help us and can only jeopardise the effort to free our colleagues and harm the family," said Jose Antonio Bastos, president of MSF Spain.
At first, the municipal council in Palafrugell, the Catalonian town where Miss Serra grew up, planned to hold a demonstration of solidarity to demand her release. However, at the request of her family, the demonstration has now been cancelled.
Blanca Thiebaut, age 30, from Madrid, was also working as a logistician for MSF at Dadaab.
She is an agricultural engineer by training and until recently was living in Barcelona. She recently studied for a degree through the London School of Economics, and has also studied in Australia.
Her father has refused to speak to the media. However, a neighbour in Barcelona told El Pais newspaper that it was Miss Thiebaut's second stint working in Africa for MSF. Her French boyfriend is also reported to be working for MSF in a different part of the continent.
Following the abduction of its two staff members, MSF suspended some of its operations at Dadaab. It is continuing essential feeding operations, but has stopped work for now on some medical services.
MSF says assistance to thousands of people in urgent need has been jeopardised as a result