NAIROBI May 11 (Reuters) - Kenya is drawing up a timetable to close Dadaab refugee camp that hosts about 350,000 Somalis because of security concerns, the interior minister said on Wednesday, after the United Nations urged the East African nation to reconsider such a move.

The East African nation, which has suffered from a spate of Islamist attacks claimed by the Islamist Somali group al Shabaab, has set up a taskforce to handle the closure plan, Interior Minister Joseph Nkaissery said.

"They will present the timetable based on all the resources required," the minister told a news conference, adding that state funds had been allocated to proceed with the programme.

"The government has commenced the exercise of closing the complex of Dadaab refugee camp," he said, without specifying what new action had been taken beyond a voluntary repatriation programme already in place.

Kenya's government has long said Dadaab, which lies near the Somali border, has been used by Islamists to launch attacks, such as the Westgate shopping mall assault in Nairobi in 2013.

Hundreds of Kenyans have been killed in that attack and other assaults mainly in Nairobi, the northeast and coast.

The Interior Ministry says it hosts 600,000 refugees, many of from neighbouring Somalia and South Sudan. Some refugees have lived in Dadaab for decades and some were born there.

Last year, Kenya said it was setting a three-month deadline to close Dadaab, but backtracked on the plan following U.N. criticism of any forced return.

Last week, the Interior Ministry said it would shut Dadaab in the "shortest time possible", prompting the U.N. refugee agency UNHCR to voice "profound concern" and renew its call for Kenya to reconsider.

The UNHCR, Kenya and Somalia signed a tripartite agreement in 2013 to repatriate Somali refugees voluntarily. As Somalia has slowly started recovering from war and chaos, Dadaab has shrunk from more than half a million people to about 350,000.

The UNHCR said in January it aimed to repatriate a further 50,000 in 2016 but also said this would be a difficult target to achieve given the Somali government is still battling an al Shabaab insurgency and there are few schools or public services.

"There has been a very slow process on the implementation of this agreement," the minister said of the tripartite deal.

(Reporting by George Obulutsa; Writing by Edmund Blair; editing by Ralph Boulton)