N’DJAMENA/NIAMEY (Reuters) - Suspected Boko Haram militants launched four attacks over 24 hours on villages in Niger, Chad and Cameroon, killing at least seven people, security and administrative sources said on Wednesday.

The Islamist militants are mostly based in northeastern Nigeria but have become a major threat to wider regional security by carrying out attacks in the lawless Lake Chad zone where the borders of Chad, Cameroon, Niger and Nigeria meet.

In the most deadly of three attacks since Tuesday, militants killed two soldiers and three civilians in Niger’s southern border town of Abadam overnight, the sources said.

About 150 km (90 miles) east in Chad, three militants were killed when they detonated suicide bombs after being found out by a group of local people as they sought to embark from an island to a lakeside market in Bol. A fourth set off his bomb but survived.

“They were intercepted by villagers who wanted to search them and they resisted,” said a local official who asked not to be named. Three other militants managed to shed the explosives they were carrying and swim away, he added.

A female suicide bomber blew herself up on Wednesday in the town of Nguetchewe in Cameroon’s Far North Region, also killing a small girl accompanying her and a local resident.

In northern Cameroon, several suspected Boko Haram fighters attacked three food trucks near the Chadian border on Wednesday, officials said. Cameroonian Special Forces (BIR) arrived shortly afterwards and there were no deaths or injuries.

Boko Haram has killed tens of thousands of people and driven more than 2 million people to flee their homes during its six-year insurgency in one of the world’s poorest regions.

Regional governments including Nigeria, Chad, Niger, Cameroon and Benin have pledged to destroy the group using an 8,700-strong regional task force. The United States has also sent troops to supply intelligence and other assistance.

But joint operations have yet to begin, leaving it up to national armies to tackle the group individually.

In the absence of effective coordination, security sources have warned this often means that soldiers just drive the militants across each other’s borders.

Both Chad and Niger have declared a state of emergency for the regions of Lake Chad and Diffa respectively which have been hit by dozens of attacks this year.

Aid agencies say they often struggle to provide food and other support to the vulnerable local populations because of the security challenges.