2 killed in blast outside U.S. base in Kabul

(CNN) - Two Afghans died when a bomb exploded outside a U.S. military base on the outskirts of Kabul on Friday morning, a spokesman for NATO-led forces in Afghanistan said.

The attack wounded four others, whose nationalities were not immediately known, a military source told CNN.

The attack about 8:30 a.m. outside Camp Phoenix appeared to be that of a suicide bomber, the Afghan Interior Ministry said. Camp Phoenix houses mostly U.S. troops who are helping train Afghan police and army forces.