Separate roadside bomb attacks killed four American soldiers in Baghdad, as American troops and Iraqi soldiers stepped up pressure on Sunni insurgents before the start of the Islamic holy month of Ramadan this week.

Last year, insurgents sharply increased their attacks against U.S. and coalition forces at the start of the holy month.

One soldier was killed in an explosion about 4:50 a.m. Wednesday in western Baghdad, the U.S. command said. The three others died in a roadside attack at about 10 p.m. Tuesday in eastern Baghdad, a separate military statement said. The names of the soldiers were withheld pending notification of their families.

It wasn't immediately clear if the soldiers were part of Tuesday's offensive, which stretched from Baghdad to the Syrian border.

A U.S. official, speaking on condition of anonymity, said there are concerns within the U.S. government about a possible rise in insurgent violence around Ramadan, because of an upswing last year �� when bombings and rocket attacks accelerated significantly in Baghdad and other areas at the beginning of the holy month.

Some militants believe they would win a special place in paradise by sacrificing their lives in a jihad, or holy war, during Ramadan, when Muslims say their sacred book the Quran was revealed to the Prophet Muhammad.

Clashes broke out in a string of militant strongholds from Fallujah, 40 miles west of Baghdad, northward along the Euphrates Valley to the Syrian border town of Qaim �� all major conflict areas. Some of the sharpest exchanges took place in Hit, 90 miles northwest of Baghdad.

Insurgents attacked an Iraqi National Guard outpost east of Qaim Tuesday, the U.S. military said. The local hospital reported 15 to 20 people were killed.

Seventy miles west of Baghdad, Iraqi troops backed by U.S. soldiers and Marines raided seven mosques in the Sunni insurgent stronghold of Ramadi, arresting a locally prominent member of a clerical association and three other people. They also seized bomb-making materials and "insurgent propaganda" in the mosques, U.S. officials said.

Source: Agencies