Story highlights Kenyan security forces crossed into Somalia and destroyed a camp, a Kenyan official says

The move was in response to an attack Saturday that left at least 28 people dead

Somali-based terror group Al-Shabaab claimed responsibility for the bus attack

Kenyan security forces have killed 100 militants, an official said Sunday, one day after a deadly attack on a bus.

Forces crossed into Somalia to launch two "successful operations on the hideouts of the perpetrators," said Kenyan Deputy President William Ruto. The camp where the attack was planned was destroyed, he said.

On Saturday, Islamist militants ambushed a bus in Kenya and sprayed bullets on those who failed to recite Quran verses, killing at least 28 people, according to authorities.

The bus, which had 60 people aboard, was heading from Mandera, near the border with Somalia and Ethiopia, to the capital of Nairobi.

About 20 miles into its dawn journey, militants stopped it at a hilly area and stormed in, local police Cmdr. Noah Mwivanda told the Daily Nation newspaper.

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Militants demanded those onboard recite Quran verses. As others watched, they opened fire on passengers who failed to do so, he said.

Somali-based terror group Al-Shabaab claimed responsibility for the attack in a statement, saying it was retaliation for mosque raids this week. It described those killed as Christians.

Al-Shabaab, which has ties to al Qaeda, has launched a series of attacks in Kenya since its forces went into neighboring Somalia in 2011 to battle the extremists.

This is one of the busiest travel seasons in the nation. Throngs make their way to relatives' homes for the holidays, with buses and other public transportation packed this time of the year.