The U.S military says four American soldiers have been killed in a roadside bomb blast north of Baghdad.

A statement says the incident occurred Thursday in Samarra, some 95 kilometers north of the Iraqi capital.

In Baghdad Wednesday, three car bombs exploded in close succession, killing at least 43 people.

Meanwhile, Iraqi political leaders are continuing negotiations on a draft constitution.

Mahmud Othman, a Kurdish member of the committee drafting the document, tells the French News agency that Wednesday's deadly bombings have increased global pressure on politicians to wrap up the constitution by the new deadline of August 22 .

He said "it has now become a question of who is stronger - the politicians or the insurgents."

Some information for this report provided by AFP and AP.