* Refugee agency freezes non-essential work in Dadaab camp
* Camp&${esc.hash}39;s ballooning numbers caused insecurity fears
* African Union condemns attack; Somali rebels blamed
(Adds detail on kidnapped Spanish women)
By Richard Lough
NAIROBI, Oct 14 (Reuters) - The U.N. refugee agency (UNHCR) said on Friday it had suspended non-essential operations at Kenya&${esc.hash}39;s Dadaab refugee camp near the border with lawless Somalia as security forces scoured the area for two Spanish aid workers kidnapped a day earlier.
Kenyan security forces fanned out through the semi-arid border area on Friday, hunting abductors believed by Kenyan police to be Somali al Shabaab insurgents. The al Qaeda-linked rebel movement has denied it was responsible for the attack.
Some aid agencies have become increasingly concerned by the worsening insecurity at the sprawling camp, where refugee numbers have swollen to more than 460,000 this year as famine and conflict drive Somalis across the border.
Nevertheless, the brazen nature of Thursday&${esc.hash}39;s broad daylight attack on two women working for Medecins Sans Frontieres in the heart of the camp stunned its relief workers.
"Today we have to hold everyone (at) base. We just have a thin staffing that is going down to the camps with a police patrol because some services cannot be suspended," said Emmanuel Nyabera, spokesman for UNHCR Kenya.
That meant there would be no registration of new arrivals, he said, but that water distribution, for example, would continue.
It was not clear when the agency&${esc.hash}39;s staff would be able to return to normal operations, Nyabera said. For now there were no plans for an evacuation of foreign staff, he added.
Medecins Sans Frontieres in Madrid said Blanca Thiebaut, 30, from Madrid, was one of the kidnapped Spanish women. The other woman, Montserrat Serra, 40, had been named yesterday. They both worked in logistics for the group at the camp.
"MSF has not been able to establish contact with the kidnapped workers so far. A crisis committee has been set up to manage the incident," Jose Antonio Bastos, president of Medecins Sans Frontieres in Spain told a news conference in Madrid.
"MSF always works without armed security... It&${esc.hash}39;s part of our policy to show people and armed groups that we have nothing to do with the conflict and we are purely a humanitarian and medical organisation," Bastos said.
The African Union strongly condemned the abduction, which came some weeks after gunmen with close ties to Somali militants kidnapped two Western visitors on northern Kenya&${esc.hash}39;s coast in separate incidents.
Kenya&${esc.hash}39;s North Eastern Province police commander, Leo Nyongesa, said the hostages&${esc.hash}39; whereabouts remained unknown. "We have contacted elders in Somalia to help us with the search."
The MSF workers&${esc.hash}39; hijacked vehicle was found abandoned late on Thursday between the Dadaab camp and the border, which lies about 100 km (60 miles) away.
The campaign group Human Rights Watch reported in 2009 that al Shabaab was recruiting fighters from inside Dadaab.
A Kenyan driver working for the international relief group Care is still missing after he was grabbed in September from the Dadaab camp.
The Geneva-based UNHCR said it has 200 staff in Dadaab. A further 100 humanitarian workers work alongside them from aid agencies including MSF. (Additional reporting by Noor Ali in Isiolo and Catherine MacDonald in Madrid; Editing by George Obulutsa and Mark Heinrich)
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