A car bomb has exploded outside an office used by US troops near the Iraqi Kurdish city of Irbil.
This is the first such attack in the relatively stable Kurdish north
One Iraqi was killed and 47 people were injured, including children in nearby houses and six US Defence Department staff.
Eyewitnesses said the man who died was a suicide bomber sitting in his car at the time of the blast.
In a separate incident, one US soldier was killed and another wounded in an ambush north-east of Baghdad on Tuesday.
The Kurdish blast happened at a checkpoint between Irbil and the nearby hilltop town of Salahuddin.
It set cars alight, and local firefighters - joined by US troops in helicopters - battled to contain the blaze and seal off the area.
The largely Kurdish north has been the most stable region of Iraq since the US-led coalition ousted Saddam Hussein in April.
Appeal for blood donors
Television pictures showed distraught local women wailing and local men running about, one of them carrying a toddler who was bleeding.
One Turkish TV reporter said the explosion brought down the front of the two-storey building.
No claims of responsibility were received after the attack, which came at 2205 (1805 GMT) on Tuesday.
Confirming the US wounded, the American military spokesman in Baghdad could not specify whether the injured were military or civilian staff.
The authorities in Irbil used loudspeakers to appeal for people to donate blood to help the injured.
The bomb vehicle, a four-wheel-drive, was completely burnt out but its chassis was still intact.
Irbil is the biggest city in the Kurdish region whilst Salahuddin is the headquarters of one of the main Kurdish factions, Massoud Barzani's Kurdistan Democratic Party (KDP).
This is the latest in a series of similar attacks including the truck and car bombs that killed the UN's Iraq envoy, Sergio Vieira de Mello, in Baghdad, and Shia leader Ayatollah Mohammed Baqr al-Hakim in Najaf.
The BBC's Owen Bennett-Jones says that such significant attacks right across Iraq pose a major challenge to US forces, which are being targeted on a regular basis.
Unknown attackers ambushed a US combat vehicle on a road north-east of Baghdad on Tuesday evening, Central Command reported.
An emergency appeal for blood went out
An "improvised explosive device" was used in the attack on a road used as major supply route.
Since the war in Iraq was effectively declared over on 1 May, at least 68 US troops have been killed by hostile fire with attacks an almost daily occurrence.
A problem for US military commanders is that providing higher levels of protection for their men frustrates their other objectives in the country, says our correspondent.
Many Iraqis now complain that US forces are concentrating more on protecting themselves than the lives and property of Iraqi civilians.