Ali al-Ubaidi, a medic at the Ramadi hospital said: "US planes bombed a house in the Aziziya area of Ramadi city centre, killing 13 civilians."
Four others were wounded, he added.
The US military confirmed it had conducted the assault, but did not immediately give further information.
Ramadi, populated by Sunni Arabs, is considered the most dangerous city in Iraq for US forces.
US ommanders say there are more attacks there than anywhere else in the country, with armed fighters and American troops exchanging fire several times a day - at least.
On Wednesday in Ramadi, a bomber exploded his vehicle near the convoy of Maamoun Sami Rashid al-Alwani, the governor of al-Anbar province, killing 10 people. The governor was not injured, US officials said.
Again on Thursday, another bomber blew himself up in Baghdad in front of a courthouse near the impoverished district of al-Sadr City, killing nine people. It was the second such attack to cause multiple deaths in Iraq in less than 24 hours.
Police first said the attack was caused by a man with explosives hidden beneath his clothing.
The man set them off in a crowd of police officers and civilians waiting outside the civil court, said police Lieutenant Thair Mahmud.
A medic from Baghdad's al-Kindi hospital said two women and a child were among the nine killed in the attack near al-Sadr City, the stronghold of Muqtada al-Sadr, an influential Shia figure. Another 50 people were wounded.
US soldiers killed
On Thursday morning, two US soldiers were killed in south- central Baghdad when their vehicle was hit by a roadside bomb, the military said.
In other violence on Thursday, armed men killed Muhammad Ridha, a brigadier in the defence ministry, in the capital's al-Yarmuk district, police said.
Iraqi police recruits were killed in
an attack in Falluja
An Iraqi soldier was shot dead near Saddam Hussein's hometown of Tikrit north of Baghdad, said the Joint Coordination Centre run by the US and Iraqi militaries.
On Wednesday, at least 15 people were killed when a bomber blew himself up amid dozens of police recruits in a queue outside police headquarters in Falluja west of Baghdad.
The latest bout of violence comes as Iraq's dominant Shia alliance said it would retain the interior ministry in the next government and the former Sunni elite demanded at least five cabinet posts.
Nuri al-Maliki, prime minister-designate, has until May 21 to name his line-up for the first permanent government of the post-Saddam Hussein era, with negotiations still going on almost five months after a December election.
Al-Maliki has said he expected the cabinet line-up to be ready by May 10.
The latest fatalities took the US military toll in Iraq since the March 2003 invasion to 2410, according to an AFP count based on Pentagon figures.