Concern is growing for a US Christian missionary kidnapped in Niger more than four months ago.

Jeff Woodke, 55, who worked for Jeunesse en Mission Entraide et Developpement, part of Youth With a Mission, was abducted by armed men from his home in Abalak in northern Niger.

His kidnappers, who murdered his guard and housekeeper, are understood to have taken him to Mali, according to World Watch Monitor.

No group has claimed responsibility but the Movement for Unity and Jihad in West Africa is thought to be behind the kidnapping.

Nigerien Interior Minister Mohamed Bazoum told AFP: 'We followed the kidnappers when they crossed the Malian border. They headed to the Menaka region (eastern Mali ), near the Niger border, an area controlled by the Mujao.'

One possible explanation is that Woodke is being held as collateral for a stolen shipment of drugs.

Woodke, from California, is a devout Christian who is open about his faith but was careful not to proselytise while working abroard. His wife and two sons, who were with him in Niger, have returned to the US. He had been working in the country for over 20 years, running projects around farming, health, literacy, education and water.

Bilou Mohamed, the mayor of Abalak, told World Watch Monitor the community had 'suffered a terrible tragedy' and locals 'wept with sorrow, lamenting the loss of a friend' the day after his abduction. He said: 'This man has lived among us for years, even in when it has been difficult to accompany vulnerable populations… Everyone knows his goodness.'