Three of Africa’s largest extremist groups are sharing funds and swapping explosives in what could signal a dangerous escalation of security threats on the continent, the commander of the U.S. military’s Africa Command said on Monday.General Carter Ham said there are indications that Boko Haram, al Shabaab and Al Qaeda in the Islamic Maghreb - groups that he labeled as the continent’s most violent - are sharing money and explosive materials while training fighters together."Each of those three organizations is by itself a dangerous and worrisome threat,” Ham said at an African Center for Strategic Studies seminar for senior military and civilian officials from Africa, the United States and Europe."What really concerns me is the indications that the three organizations are seeking to coordinate and synchronize their efforts,” Ham said. "That is a real problem for us and for African security in general.”The United States classified three of the alleged leaders of the Islamist sect Boko Haram, based in remote northeast Nigeria, as "foreign terrorist,” on June 20. But it declined to blacklist the entire organization to avoid elevating the group’s profile internationally. Police in Nigeria said members of the group seized a prison there Sunday and freed 40 inmates.Islamist militant group al Shabaab is active in war-ravaged Somalia and has been blamed for attacks in Kenya. Last year it claimed responsibility for the death of Somali Interior Minister Abdi Shakur Sheikh Hassan.Al Qaeda in the Islamic Maghreb (AQIM), an affiliate of al Qaeda based in North Africa, is mainly a criminal organization operating in the Sahel region. It kidnaps Westerners for ransom and aids Africa’s drug trade, according to intelligence officials.