Gunmen raided the house of a US aid worker in central Niger overnight, killing his two guards before driving him off across the desert towards Mali, the mayor of the town said on Saturday.

According to French news outlet Radio France Internationale, the victim worked for Christian missionary organisation Youth With A Mission (YWAM).

"First they came on a motorbike and killed the guards," the mayor of Abalak, Ahmed Dilo, told Reuters by telephone. "Then a 4x4 came and took him away and drove towards the Mali border."

Residents reported hearing gunfire near the aid worker's house, where he had been living for years. Dilo said a Nigerien soldier was among the guards killed.

Witnesses told CNN that the victim was forced to strip down to his underwear before he was taken away, which is a tactic sometimes used by abductors to stop hostages from being tracked.

Kidnappings of foreigners in Niger are rarer than in neighbor Mali, where Islamist militants are active and often seize hostages for ransom or political capital.

The militants and allied criminal gangs have long exploited the largely unpoliced desert spaces of the Sahara and attacks have increased this year as security worsens in Mali.

No US citizen has been kidnapped in Niger before, although in 2009 suspected Islamists attempted to abduct US embassy personnel from a hotel in the town of Tahoua.

A US embassy spokeswoman said there was an investigation into the incident but could not confirm any additional details. Niger security forces did not immediately comment.

YWAM is a Christian missionary organisation that has teams all over the world.

Christian Today has approached YWAM's office in Mali.

Additional reporting by Reuters.