The gunmen burst into the churches in apparently coordinated attacks targeting worshippers as they held Sunday prayer services in Garissa, some 140 kilometres (85 miles) from the border with war-torn Somalia. The attackers later escaped.

"At the AIC (Africa Inland Church) 10 people were shot dead within the church compound, and three were injured in a Catholic Church," said deputy regional police chief Philip Ndolo. "We condemn this act in the strongest of terms."

Police said that as many as seven men were involved in the attacks, which come two days after gunmen killed a Kenyan driver and abducted four foreign aid workers from the Dadaab refugee camp, some 80 kilometres (50 miles) northeast of Garissa.

"We have not arrested any suspects, but we have reports that five suspects were involved in the AIC attack in a combination of grenade and shooting, while two suspects were involved in the Catholic church attack," said Ndolo.

Witnesses said that bodies lay scattered in the blood spattered churches as scores of wounded were rushed to hospital.

"It is a terrible scene, you can see bodies lying in the churches," said regional police chief Leo Nyongesa, adding the attackers had wrested guns off police, who have been posted outside churches following previous attacks.

It was not clear who was behind the attacks, but Nairobi has blamed similar attacks on members or supporters of Somalia's Al-Qaeda linked Shebab insurgents.

Kenya has suffered a spate of grenade attacks, shootings and bomb blasts since sending troops into southern Somalia in October to crush Shebab bases there, prompting warnings of revenge attacks by the Islamist fighters.

The Supreme Council of Kenya Muslims condemned the attacks, saying that "all places of worship must be respected."

"We want to send our condolences, and we are sad that no arrests have been made yet," said chairman Abdulghafur El-Busaidy.

The attacks come as search efforts continued for the abducted aid workers, two men and two women who work with the Norwegian Refugee Council (NRC), and who come from Canada, Norway, Pakistan and the Philippines, according to police.

But while Kenya's army scoured border areas for a third day, many fear the gunmen and their hostages crossed swiftly into Somalia, only some 100 kilometres from Dadaab where they were seized, the word's largest refugee camp.

Attacks and cross-border raids in the region blamed on the Shebab, including the kidnapping in October of two Spaniards working for Medecins sans Frontieres (Doctors Without Borders), were key to Kenya's decision to invade Somalia.

The Shebab still control large parts of southern Somalia, despite recent losses to African Union troops, government forces and Ethiopian soldiers, who have wrested several key bases from the insurgents.