Story highlights

Suicide bombers in vehicles started the raid, a source said

Some Kenyan troops have died, Kenya's President confirms

CNN  — 

Kenya’s President vowed retribution Friday after Al-Shabaab fighters attacked an African Union base in Somalia, killing an unknown number of Kenyan troops serving with the African Union force fighting the militant group.

“We will hunt down the criminals involved in today’s events,” Kenyan President Uhuru Kenyatta tweeted Friday. “Our soldiers’ blood will not be shed in vain.”

The pre-dawn raid in El Adde in southwestern Somalia began with explosions from two car bombs driven by suicide bombers, a source told CNN.

AMISOM said in a statement its troops turned the attack back but some of its forces had been killed and others wounded.

The AMISOM statement didn’t say how many soldiers had been killed, but a source within the Somali security service told CNN on condition of anonymity that Kenyan forces stationed at the base had suffered “significant casualties.” At least 18 vehicles were destroyed, the source said.

The Kenyan position was overrun, the Somali source said.

The Kenyan Defense Ministry said in a statement that only Somali forces were overrun.

There was no immediate indication of Somali deaths or injuries.

Gedo regional Gov. Mohamed Abdi Kalil tweeted Friday that Kenyan and Somali forces were still in control of the town.

He said that Al-Shabaab claims of large-scale casualties among AMISOM troops were “total propaganda.”

In a series of tweets Friday, Kenyatta expressed gratitude for the sacrifice of the slain Kenyan soldiers, calling their deaths “heartbreaking.”

“I express mine and the country’s deepest sympathy to the families and the loved ones of the fallen,” Kenyatta wrote. “I stand with you. Our country stands with you.”

Robyn Kriel reported from Nairobi, Kenya. Michael Pearson reported and wrote from Atlanta. CNN’s Brianna Duggan, Radina Gigova and Merieme Arif contributed to this report.