A disgruntled former employee shot at least two international workers from the aid group Doctors Without Borders at the group's office in the Somali capital, a security guard said Thursday. At least one person was killed.

Ahmed Ali, a security guard for the aid group which is known by its initials in French as MSF, said a Somali employee who ran its logistics was dismissed from his job on Wednesday. He returned on Thursday and opened fire, hitting the two aid workers, killing one of them, Ali said. Details were sketchy.

A Nairobi, Kenya-based security official said he believed three international workers had been shot. The security official spoke on condition he not be identified because the information hadn't yet been released publicly.

The nationalities of the aid workers weren't immediately known.

A Doctors Without Borders spokeswoman said she had no immediate comment.

Mogadishu is one of the most dangerous locations for aid workers to conduct business. Many groups don't allow international workers to stay in the capital for long and rely primarily on Somali employees. International aid workers face potential attacks from militants and kidnappings for ransom.