MAIDUGURI, Nigeria, Oct 2 (Reuters) - Suspected Boko Haram Islamist militants killed at least 18 ​villagers who had gone into the ‌bush to collect firewood in Nigeria's northeastern Borno state, local leaders and security sources said.

Other ​villagers were still missing after the ​attack on Thursday in Marte Local ⁠Government Area, one of the areas hardest ​hit by a 17-year-old insurgency.

Armed groups — some ​seeking to carve out a Caliphate in the region, others seeking plunder or ransoms and recruits from ​kidnappings — have killed tens of thousands ​of people and displaced millions in regular raids.

Villagers ‌have ⁠come under attack as they stray into rebel areas while pushing into the bush for farming and firewood.

The traditional ruler ​of Marte ​said 18 ⁠bodies had been recovered after the attackers ambushed the villagers.

A ​senior military officer said troops had ​launched ⁠clearance operations in the area and were pursuing the attackers.

The insurgency in northeastern Nigeria ⁠is ​led mainly by Boko ​Haram and its offshoot, Islamic State West Africa Province.