<p>BAGHDAD — An attacker, his body wrapped in explosives and his car filled with 50 pounds of TNT, struck a police checkpoint outside U.N. headquarters in Baghdad yesterday, killing an Iraqi policeman who stopped him and wounding 19 persons.</p>
<p>A U.S. military spokesman at the scene said the bomber, who also died in the 8:10 a.m. blast, was trying to get into the U.N. compound at the Canal Hotel, where a truck bomb a month ago killed 23 persons including the top U.N. envoy to Iraq, Sergio Vieira de Mello. Yesterday's attack wounded two U.N. workers.</p>