KABUL, Afghanistan (AP) — A suicide bomber blew himself up at a park today in northern Afghanistan, killing at least 10 people, including three NATO service members, officials said, the latest in a string of attacks as spring fighting season gets under way.

Afghan and NATO security forces have frequently been targeted in the surge of violence as militants fight to assert their power and undermine U. S. efforts to try to build up the Afghan military and leave combat responsibility to local forces by the end of 2014.

The bomber was riding a motorcycle when he detonated his explosives at the gate of the park in Maimanah, the capital of Faryab province, police spokesman Lal Mohammad Ahmad Zai said. It was not clear what was targeted, but he said four of those killed were police officers.