Three powerful car explosions shook central Baghdad on Monday, including two hotels used by international reporters and foreign contractors; the Palestine and Sheraton hotels, police said, according to BBC.
The attacks killed more than 17 people, mainly security guards, hotel employees and passers-by. At least nine people were wounded.
The blasts, which took place shortly after the evening breaking of the Ramadan fast, blew out windows and damaged buildings.
Correspondents said the explosions scattered shrapnel and debris over a wide area beyond the high-rise concrete towers of the hotels.
The Associated Press reported that a U.S. armored vehicle was damaged in one of the explosions but it was empty at the time.
After the attacks, automatic heavy weapons fire rang out in the area although it was not clear what it came from.
Iraq's national security adviser, Muwafaq al-Rubaie, said the attacker had apparently wanted to seize the Palestine Hotel and take reporters hostage but he did not say what evidence he had to back such a plan.
Earlier Monday, police in Baghdad said they found in the last 24 hours the bodies of seven people, including three women, dumped in and around the city.
In other violence, two people were killed in a car bomb blast near an Iraqi police patrol in Baghdad on Monday.
The explosion took place in the north-eastern district of Shaab, where rebels abducted and killed one of Saddam Hussein's defense lawyers last week.
Meanwhile, twelve construction workers have been shot dead south of Baghdad on Monday, Iraqi police said.
All the men were shot in the head and chest shortly after leaving a building site near the town of Musayyib, BBC reported.
The violence comes amid speculation the referendum on the new Iraqi constitution may fail.
Two Sunni-dominated provinces have rejected the constitution, according to preliminary results given by election officials.
The charter will fail if three out of the 18 provinces vote "No" by two-thirds or more and all eyes are on the province of Nineveh, where the result is expected to be announced within two days.
In a separate development, a former Iraqi security official, ill with cancer, testified in Saddam Hussein’s trial.
Former intelligence officer Waddah al-Sheikh gave a statement in hospital on Sunday about the killing of 143 people in the town of Dujail in 1982.
A court official said they "have recorded the testimony of this individual.”
"His words were recorded and written down on paper."
Sheikh, who was working for Iraq's main intelligence agency at the time of the Dujail massacre, is considered one of the main witnesses in Saddam’s trial. He is suffering from cancer and there are fears that he may not have long to live.
Saddam is charged with the killing of at least 149 men in the mostly Shiite town of Dujail after a failed assassination bid against him.
The toppled Iraqi President and seven other defendants have pleaded not guilty to the charges.
The trial was suspended until November 28 after several prosecution witnesses failed to turn up for the opening day on 19 October.