ABUJA, April 16 (Xinhua) -- A conference co-hosted by the U.S. military and aimed at boosting cooperation between military forces of countries fighting extremist groups opened in the Nigerian capital Abuja on Monday.

　　Top military officers from at least 30 African countries and some top military chiefs from the United States and Europe attended the opening session of the sixth African Land Forces Summit, with the theme "Unity in Strength: Combating Africa's Security challenges."

　　The military leaders exchanged notes on threats in Africa, from al-Shabab in the east to Boko Haram in the west.

　　At the opening, Nigeria's defense chief Abayomi Olonisakin urged Africa's army chiefs to develop and adopt a united approach to confront various emerging security threats on the continent.

　　Olonisakin noted that a united approach became imperative as global security threats had continued to be volatile, uncertain, complex and ambiguous.

　　"Terrorism, human trafficking, the proliferation of small arms and light weapons, as well as piracy, have continued to pose security challenges to our individual and collective countries," he said.

　　The Nigerian defense chief also said there was the need to acquire fighting capacity through training, intelligence sharing, and acquisition of equipment among the various armies, adding the summit might provide the continent's army chiefs with new ideas and ways to tackle the numerous challenges bordering on security and military professionalism.

　　Curtains will fall on the four-day summit on Thursday, followed by a joint press conference by the military leaders of the participating countries.