Members of the Somalian rebel group al-Shabab have abducted two female Spanish aid workers from Kenya's Dadaab refugee camp, a regional police official has said.

"Two aid workers of Spanish nationality have been kidnapped by the Shabab, they are working for MSF (Medecins Sans Frontieres)," Leo Nyongesa, regional police chief, told the AFP news agency on Thursday.

Al-Shabab has denied any involvement in the kidnapping.

The district commissioner of Dadaab told Al Jazeera that MSF staff usually travel without security escorts. He said military helicpoters had begun a search for the aid workers.

Al Jazeera's Nazanine Moshiri, reporting from Nairobi, said the aid workers' Kenyan driver was shot in the neck, but was in a stable condition.

"The border area has been closed, and they are searching for the women using military helicopters," she said.

"The problem is, this kidnapping happened quite a while ago and there are smuggler routes which the Somalis do use and these two women could be in Somalia by now."

Safety at camp

The head of MSF-Spain said that the organisation strongly condemned the attack and was in contact with relevant authorities to ensure the women's "swift and safe return".

Currently the world's largest refugee camp, Dadaab hosts at least 380,000 Somalis fleeing the severe drought that killed livestock and destroyed crops.

The recent kidnapping, along with the abduction three weeks ago of a Kenyan driver working for Care Kenya, has raised questions about the safety of aid workers.

Analysts believe the recent escalation of kidnappings could represent a new tactic by al-Shabab fighters who have experienced heavy blows in the recent offensive by African Union troops and soldiers from Somalia's transitional government.

In recent weeks, a French woman and a British tourist were also kidnapped in separate incidents near the border with Somalia.

Gunmen took the French woman from her home near the resort town of Lamu on October 1.

Kenyan authorities gave chase but said the kidnappers escaped into Somalia. The government blamed al-Shabab.

In early September, attackers believed to have been Somali pirates shot dead a British man and kidnapped his wife from a resort north of Lamu.

Pirates have long sought ransoms in the millions of dollars for high-value hostages typically taken at sea.