At least 21 people, including 15 soldiers, were killed in separate overnight encounters in India 's restive northeast Manipur Pradesh, officials Tuesday said.

In the first incident, heavily armed militants ambushed a security patrol of the Gorkha Rifles near Nariang village, about 35 km from Imphal, capital of Manipur late Monday.

"Unidentified rebels using automatic weapons ambushed a road patrol of the army's Gorkha Rifles, killing eight on the spot," Indo-Asian News Service quoted an Indian Army spokesperson as saying. Twelve more soldiers were wounded, of whom six died on way to hospital.

The 20 odd rebels equipped with AK-56 rifles and carbines launched the attack from a hilltop. It was hard for the soldiers to retaliate at any time, said the spokesperson.

The identity of the rebels is not immediately known and no militant group has claimed responsibility for the ambush as yet.

In the second incident, rebels belonging to the outlawed United National Liberation Front (UNLF) killed an Indian army soldier near Jiribam, Manipur's border town with Assam state.

In a third incident, six tribal militants were killed in a faction fight between two groups in Churachandpur district.

There was a massive clash between the Zomi Revolutionary Army and the Zomi Revolutionary Front over territorial supremacy. In the ensuing gun battle, six rebels were killed and another was wounded, local police official said.

There is a score of rebel groups in Manipur, bordering on Myanmar, with demands ranging from secession to greater autonomy and the right to self-determination. More than 10,000 people have lost their lives to insurgency in Manipur during the past two decades.

Source: Xinhua