NAIROBI, Nov. 19 (Xinhua) -- The Kenyan government has issued an ultimatum to the Somali Islamists fighting the transitional government of Somalia to unconditionally return two Italian Catholics nuns they abducted a week ago in northeastern Kenya town of Mandera.

    Internal Security Minister George Saitoti told a news conference late Tuesday that the government will be relentless in protecting its borders from Somali militant attacks.

    "They stole three government vehicles, are you now telling me that we should sit down and let those people to come and violate our borders," Saitoti told journalists in Nairobi.

    "We will deal with them effectively, we have given an ultimatum to them to return them and we are very firm on that one," he said after holding talks with visiting British Armed Forces Minister Bob Ainsworth.

    Saitoti gave a 24-hour ultimatum to the Al-Shabaab militia that has engaged the transitional government in running battles.

    "Time is running out for the militia and they must free the nuns," said the minister.

    The militia crossed into Kenya from Somalia and attacked Elwak town in Mandera. They fled with the three vehicles, two of which were ferrying Kenya Certificate of Primary Education exam papers.

    The two nuns were kidnapped from a dispensary in Elwak. The Italian nuns are Sisters Maria Teresa Olevero and Catarina Giraudo.

    Saitoti said security forces had been deployed to Mandera to rescue the nuns. "We will not sit and watch as foreigners violate our borders," said Saitoti. He said the border between Kenya and Somalia was closed, adding security forces had been deployed there.

    "They violated the sovereignty of this country by crossing the border and abducting the two nuns and three drivers, we cannot allow this to happen." The minister said the government will maintain a massive security operation at the Kenyan-Somali border until the two nuns are traced alongside the three drivers.

    He also said the militiamen must return three government vehicles that they stole during the raid. Reacting to reports that families were fleeing their homes in Mandera following a security operation in the area, Saitoti defended the exercise, saying it will continue.

    "It should not be surprising to any person that we do have beefed up security around that border. And we have no apologies to make. The security is there to deter those who want to violate laws and cross to our border, they are not there to molest any Kenyans at all," he said.

    The minister further said the Kenyan-Somali border would remain closed until security is improved, noting that cattle rustling was a challenge that the government had to deal with.

    "This menace has almost become a norm among pastoralist communities, and this has to be brought to an end," he said. The minister said he has been holding meetings with security officials and leaders from the affected areas to seek ways to resolve the issue.

    In addition, Saitoti said the military operation in Mandera called to contain clan fightings had been scaled down to allow for peace talks between the clans, political and religious leaders from the region.

    He said the operation was successful and had led to the recovery of weapons. The clan fights sparked by disputes over pasture and watering holes for livestock led to the death of over 20 people.

    Saitoti said security had also been beefed up in Nairobi's Central Business District, following a wave of robberies targeting at businesses. "The robberies have to come to an end. The criminals are being hunted down," said Saitoti.