At least 49 people have been killed after militants from Somalia's Al-Qaeda-linked Shebab stormed into a Kenyan coastal town, attacking a police station, hotels and homes and singling out non-Muslims for execution, officials and witnesses said on Monday.
The assault on Mpeketoni, near the coastal island and popular tourist resort of Lamu, was the worst attack on Kenyan soil since last September's siege of the Westgate shopping mall in the capital Nairobi.
A statement from the Shebab said the latest brazen attack was further retaliation for Kenya's military presence in Somalia as well as the "Kenyan government's brutal oppression of Muslims in Kenya through coercion, intimidation and extrajudicial killings of Muslim scholars."
The group also declared Kenya a "war zone" and warned tourists and foreigners to stay out of the country.
Witnesses said a group of around 50 attackers in several vehicles entered the town late Sunday, attacked a police station before moving on to kill civilians, some of whom had been watching the World Cup in local bars and hotels.
"Women and children were put aside. All of those who were killed were Christians. If you were a Muslim you were spared," said John Mwagi, a 44-year-old teacher who witnessed the attack.
"They were chanting slogans, Allahu Akbar ('God is Greatest'). I saw their flag carried by a small boy."
The manager of Mpeketoni's New Breeze hotel, which was burned down in the attack, also saw the attackers singling out non-Muslims -- something the Shebab also did during the Westgate attack.
"They asked women and children to stand aside and the men to get down, and asked if they knew how to pray. They were speaking Somali," the manager, John Wanyoike, told AFP.
Police spokeswoman Zipporah Mboroki confirmed that 49 people had died, including at least one police officer.
Charred buildings in the town -- which is around 100 kilometres (60 miles) from the border with Somalia -- still smouldered a day after the attack, including hotels, restaurants, banks and government offices.
Resident Anne Gathigi, 38, a mother of five, said the attackers killed her husband.
"They forced their way into our house, found us in the bedroom. They picked up my husband and took him to the sitting room where they demanded money from him, as soon as he gave them some cash, they shot him at close range," she recounted.
"They told me since 'our government has refused to pull our soldiers from Somalia', they had come to leave us 'widows and orphans'."
Kenyan troops crossed into southern Somalia in 2011 to fight the Shebab, later joining the now 22,000-strong African Union force battling the militants and supporting the war-torn Horn of Africa nation's internationally-backed but fragile government.
In Nairobi, Kenya's embattled Interior Minister Joseph Ole Lenku called the killings a "heinous act" and told reporters that security has been beefed up across the country.
But the Shebab said more attacks would follow in Kenya.
"To the tourists visiting Kenya we say this: Kenya is now officially a war zone and as such any tourists visiting the country do so at their own peril," a statement from the group said. "Foreigners with any regard for their safety and security should stay away from Kenya or suffer the bitter consequences of their folly. You have been forewarned!".
"We hereby warn the Kenyan government and its public that as long as you continue to invade our lands and oppress innocent Muslims, such attacks will continue and the prospect of peace and stability in Kenya will be but a distant mirage. Do not ever dream of living peacefully in your lands while your forces kill the innocent in our lands," it added.
Last month the Shebab also carried out a restaurant bombing in Djibouti and has in the past attacked Uganda and Ethiopia, countries which also contribute to the AU force in Somalia.
The town of Mpeketoni, a trading centre on the main coastal road, lies on the mainland some 30 kilometres (20 miles) southwest of Lamu island, a popular tourist destination whose ancient architecture is listed as a UNESCO World Heritage site.
Hundreds of British tourists were also evacuated last month from beach resorts near Kenya's port city of Mombasa following warnings of imminent terror attacks from Britain's Foreign Office.
Britain this week released warnings to citizens in several East African nations -- including Djibouti, Ethiopia, Kenya and Uganda -- citing the threat of attacks at public screenings of the World Cup.