Muhammad Jalal, a doctor in the neighbouring town of Falluja, said on Wednesday: "We have the bodies of five Iraqis and four foreigners... In addition, 10 injured Iraqis were admitted to our hospital."
The doctor was unable to determine the nationality of the dead foreigners.
Citing the local rescue services, he added that the four had been travelling in an all-terrain vehicle, typically favoured by US-led occupation forces in Iraq, which was badly damaged in the explosion.
The US military said a blast took place in eastern Ramadi at around 0445 GMT but added that, according to initial reports, only five Iraqis were injured and there were no "coalition" casualties.
It was unclear whether the two reports were about the same attack.
US marines arrested six members of the Iraqi Civil Defence Corps on suspicion of involvement in the bombing, along with an Iraqi civilian who ran out of a nearby building after the blast carrying hand grenades, a military spokeswoman said.
The seven were taken to an occupation force base for questioning.
"We have the bodies of five Iraqis and four foreigners... In addition, 10 injured Iraqis were admitted to our hospital"
Doctor in Falluja
The military spokeswoman said the device was contained in a fuel drum, which sprayed burning fuel and oil on several nearby cars when it exploded.
A witness said an explosion took place at 0530 GMT in front of a mosque in the centre of Ramadi.
"After hearing the explosion we ran to the site and saw corpses and injured people," said merchant Muhammad Jabr.
Jabr said the explosion was caused by a roadside bomb, adding that security services soon arrived at the scene to deal with the casualties.
A second witness, Samir Hammadi, said he believed the bomb had been placed amongst oil cans that were being sold on the roadside.
Ramadi has been a hotbed of anti
Ramadi, near the rebel bastion of Falluja, has been a hotbed of insurgency against US-led occupation forces.
During heavy clashes against marines in April, some troops from the US-formed ICDC defected to join the rebels.
The attack came just two days after a car bombing on an occupation force convoy in Baghdad killed 13 people, including five foreigners, and wounded 69.