Two American military trainers were killed and a third wounded in a shootout with security guards at a Jordanian military base south of the capital, reports the AP. No official explanation has emerged about what happened, but a Jordanian military source tells Reuters that the Americans failed to heed orders to stop at the base's entrance gate. A source confirms that version of events to CBS News, which notes that Jordan is a strong US ally and attacks on Americans there are rare. A Jordanian military officer was reportedly wounded in the shootout. No identities have been released. (More Jordan stories.)