BENGHAZI, Libya -- A suicide car bomb at a security checkpoint in eastern Libya on Sunday killed at least seven people and injured about 15 others, according to medical and security officials.

The powerful explosion took place in Bersis, about 30 miles from the increasingly restive city of Benghazi. An American schoolteacher was killed in Benghazi earlier this month, and the city was the scene of the September 2012 attack on the American consulate that killed the U.S. ambassador to Libya, J. Christopher Stevens.

Several heavily armed groups operate in the city and its environs, and have been battling one another and the security forces. Assassinations and bombings are favored tactics; Benghazi's military chief was assassinated last week.

A number of diplomatic missions in Benghazi have closed as a result of the recent bout of violence, which has wreaked havoc in the country's oil industry. The rival militias sprang up in the wake of the 2011 fighting that toppled and killed longtime leader Moammar Kadafi, with the country's oil-rich east a key prize.

Militias have seized control of ports and oilfields in and near Benghazi to try to win concessions from the weak central government of Prime Minister Ali Zidan. The government has made little headway in efforts to rein in the armed groups, whose influence has spread to the capital Tripoli as well.

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Juma is a special correspondent. Staff writer Laura King contributed to this report from Cairo.