The commander of government troops fighting Ugandan Islamist rebels in eastern DR Congo has been killed, a government spokesman said.Colonel Mamadou Ndala died along with two bodyguards in an ambush in North Kivu province, the spokesman said.It appeared to be the work of the rebel Alliance of Democratic Forces and National Army for the Liberation of Uganda (ADF-Nalu), he added. DR Congo, with UN help, is trying to crack down on armed groups in the area.There are believed to be at least 10 such groups, ADF-Nalu is considered to be the only Islamist organisation."This is really an immense loss for the armed forces and the republic,” government spokesman Lambert Mende told AFP news agency. The ADF-Nalu was blamed for a brutal attack on civilians in villages around the town of Beni last month.At least 40 people - including women and children - were killed. Most appeared to have been hacked to death and three girls had been raped and then beheaded.