BAGHDAD (AP) – Two suicide car bombers attacked a market and a police checkpoint on the outskirts of Ramadi, killing at least 20 people and dealing a blow to recent American claims of success in reclaiming the Sunni city from insurgents.

The violence came a day after roadside bombs killed eight American soldiers, including six who died in a single blast in the surrounding province of Diyala. The mounting American casualty toll highlights the dangers facing troops as they take to the streets more as part of a security crackdown in the Baghdad area.

The first attack targeted a public market about noon northwest of Ramadi, 70 miles west of Baghdad, killing 10 civilians and wounding about 30, police said.

About 15 minutes later, another bomber detonated his vehicle at a nearby police checkpoint, killing five police officers and five bystanders and wounding 10 others, police said.

The American military has struggled for years to secure Ramadi, the capital of the insurgent stronghold of Anbar province.

The city has shown recent signs of calming, with whole neighborhoods being walled off and military units moving off the major bases and establishing smaller American-Iraqi posts in the most violent areas downtown. But the violence has continued as insurgents fight back for control.

Violence also has surged north of Baghdad, where militants have fled the security crackdown in Baghdad that began on Feb. 14.

A bombing and an ambush in Baqouba, a Sunni insurgent stronghold northeast of Baghdad, killed two soldiers and two policemen Monday as militants apparently step up a campaign against Iraqi security forces.

The attacks began about 4:30 a.m. when a booby-trapped house exploded during a raid, killing two Iraqi soldiers and wounding three. About six hours later, gunmen ambushed a police station elsewhere in the city, killing two officers and wounding two others, police said.

The bullet-riddled body of a policeman bearing signs of torture also was found outside the northern city of Kirkuk.