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MOGADISHU, Sept 23 (Reuters) - Somali gunmen have abducted two foreigners working for the aid agency Medecins du Monde along the border with Ethiopia, the organisation and witnesses said on Tuesday.

Kidnapping of foreigners and aid workers has become common in Somalia, where a transitional government is fighting Islamist insurgents and clan militia rule large areas. Most hostages are freed unharmed after ransom payments or negotiations.

"All we are confirming at this point is that indeed two of our people have been taken, that they were expatriates and that we are in contact with authorities," Susan Wright, the director of MDM UK, told Reuters from London.

In France, the organisation issued a statement saying that the two employees, who were on a mission in Ogaden region, were abducted on Monday and that it was in constant contact with the authorities.

The pair were grabbed at the border village of Laas Caanood on Monday night and taken to Gurael, about 500 km (300 miles) north of the capital Mogadishu, locals said.

"Two white people, a man and a woman, were brought to Gurael district last night from the Ethiopian border by about 10 well-armed Somali clan militia," said resident Salad Abdi, adding they were Western aid workers.

Authorities said they were on the case.

"We have heard that some kidnapped people were brought here last night ... we are investigating the issue," deputy district commissioner Osman Taar Gurael told Reuters.

"We do not know where they have been taken," he added.

Ethiopia's Ogaden National Liberation Front (ONLF) rebel group, which operates near the border, condemned the kidnap, saying it aimed to undermine international aid efforts in the region hard hit by famine.

"ONLF will do its outmost to free the humanitarian workers and will not rest until the culprits are dealt with in an appropriate manner," the group said in a statement.

MDM operates mobile health clinics in Somalia to prevent epidemics among those displaced by fighting. (Additional reporting by Tamora Vidaillet in Paris) (Writing by Wangui Kanina, Editing by Jon Boyle)

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