United States announced it will deploy four additional combat battalions to Baghdad, as Pentagon officials are planning to boost the U.S. troop level in Iraq by sending another 3,500 soldiers to Baghdad to help restore security there, Defense Department officials said Wednesday, International Herald Tribune reports.

The decision to send more troops to Iraq, announced by Pentagon officials, follows the continuing increase of violence in Iraqi streets.

Meanwhile, the White House expressed its doubts about Iraqi Prime Minister Nouri al-Maliki to handle the sectarian violence in his country.

The New York Times published the text of a memo from a top White House adviser expressing doubts about the prime minister's ability to rein in the sectarian violence.

"His [Maliki's] intentions seem good when he talks to the Americans, and sensitive reporting suggests he is trying to stand up to the Shia hierarchy and force positive change", the memo written by adviser Stephen Hadley says, as quoted by the New York Times and ABC News, among others.

"But the reality on the streets of Baghdad suggests Maliki is either ignorant of what is going on, misrepresenting his intentions or that his capabilities are not yet sufficient to turn his good intentions into actions."

U.S. President Bush initially planned to meet with Maliki on Wednesday, but the meeting was postponed for one day. Some reports suggested that the delay was caused by Iraqi leader's fury over the release of the explosive memo.

The increase in the American military presence in Iraq has not been formally approved by the Bush administration yet.

The final decision could be made in the next few weeks. The first of the additional troops may begin arriving in Iraq early next year. The units will consist of military engineers and additional combat power.

So far, U.S. involvement in Iraq now exceeds the length of America's participation in World War II.