Iraq’s political crisis deepened Sunday as Prime Minister Nouri al Maliki ordered the country’s vice president off a plane and had him held temporarily at Baghdad airport, on suspicion that members of his security detail took part in a string of assassinations.

The confrontation between the prime minister, a Shiite Muslim, and Vice President Tariq al Hashimi, a Sunni, took the spotlight off of what could have been a day of Iraqi unity and celebration as the last American tanks and troops rolled south to Kuwait, ending the nearly nine-year U.S. military presence.