Shebab militants killed at least 14 workers in northern Kenya on Tuesday, officials said, the latest in a wave of attacks in the east African nation by the Somali-led Islamists.

The attack occurred just outside the town of Mandera in Kenya's far northeastern region, which borders Ethiopia and war-torn Somalia, and comes a little more than two weeks before U.S. President Barack Obama is due to make his first presidential visit to Kenya, where his father was born.

Five men arrested in connection with the Garissa university massacre in April were charged in a Kenyan court on Thursday with terrorism, officials said.

The charge sheet read out to the suspects stated that they conspired to commit a terrorist act on April 2nd, on the day 148 people -- most of them students -- were killed at the college.

Kenyan police have fought a fierce battle with Shebab militants after an ambush near the border with Somalia, officials said Tuesday.

The militants claimed in a statement that at least 20 police were killed, although Kenyan authorities insisted that only five officers were wounded, with Interior Minister Joseph Nkaissery dismissing claims of fatalities as "propaganda".

U.S. Secretary of State John Kerry vowed support to Kenya on Monday in the battle against Somalia's al-Qaida-affiliated Shebab, after calling for unity in the face of terror attacks.

"The U.S. continues to stand resolutely with the government and people of Kenya in the effort to end scourge of violent extremism," Kerry said.

Gunmen killed 10 people and wounded dozens when they opened fire and hurled grenades into two churches in the eastern Kenyan town of Garissa on Sunday, the latest in a string of attacks, police said.

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

Five people were killed in a New Year's Eve hand grenade attack and shooting in a bar in the eastern Kenyan town of Garissa near the border with Somalia, police said Sunday.

"There was an explosion in a club in town shortly before midnight (Saturday) and five people died," a senior police officer at Northeast provincial headquarters told AFP.