U.S. Defense Secretary Robert Gates made an unannounced visit to Iraq on Wednesday to assess the progress that has been made in recent months since the buildup of U.S. forces began to take hold and reduce violence in some parts of the country.

Making his sixth trip to the battlefront in a year, Gates planned to talk to Gen. David Petraeus, the top military commander in Iraq, and also meet with Iraqi Prime Minister Nouri al-Maliki.

He was last in Iraq around Labor Day, in a joint surprise visit with U.S. President George W. Bush.

"Secretary Gates is here to see for himself the considerable progress that has been made since his last visit nearly three months ago now, just before Gen. Petraeus offered his assessment of the situation to the American people," said Pentagon press secretary Geoff Morrell, who is traveling with Gates.

Morrell said Gates wants to "get their take on the situation and to see what more they can do to capitalize on the gains that have been made since the surge of U.S. forces in Iraq."

Gates visit comes as U.S. force levels begin a slow decline, with the plan to reduce the number of combat brigades in Iraq from 20 to 15. One brigade left in recent days and is not being replaced, leaving about 162,000 U.S. troops in Iraq.

Gates' six visits to Iraq have all come since he became Pentagon chief about a year ago. The military buildup began a short time later, and while some violence and bombings have spiked, there has been a downturn in attacks and casualties in recent months.

Gates has suggested that he would like to see the number of troops dropped to about 100,000 by the end of next year. The reduction in brigades would likely only bring the troop totals to about 160,000 or so by midyear.

There are about 3,500 troops in a brigade.