Niamey, Feb 11 (IANS): Over 500 Boko Haram fighters have been killed by Niger's defence forces supported by Chadian troops between last Friday and Tuesday, eyewitnesses have said.

The eyewitnesses and workers of humanitarian agencies said over 200 decomposing bodies of Boko Haram militants were seen strewn all over near Kamadougou river which marks the border between Niger and Nigeria, after the first attack Friday, Xinhua news agency reported.

It was on Friday that Boko Haram fighters invaded Niger's Bosso locality near the Nigerian border.

However, due to the firepower of the Nigerian troops supported by Chadian soldiers, majority of the fleeing assailants were gunned down in clashes that lasted for several hours.

Following the Islamists' second attempt to attack Niger's Diffa town, the Nigerian army launched an air offensive against the group's bases in the Nigerian towns of Damasak and Doutchi, forcing them to flee from these towns that they had controlled for a long time.

The retaliation, both on the ground and from the air, resulted in heavy losses among the Islamists, security sources said.

Despite the heavy losses suffered by the Boko Haram, the group has continued to launch attacks in the town of Diffa where the Nigerian government has declared a 15-day state of emergency starting Wednesday.

On Monday, the Nigerian parliament unanimously adopted a resolution authorising the government to deploy troops to Nigerian territory to fight the Boko Haram.