WASHINGTON, May 22 (Xinhua) -- The Pentagon is considering maintaining a core group of forces in war-battered Iraq, possibly for decades, despite increasing pressure from the Congress and the public to pull out, NPR radio said on Tuesday.

    A number of U.S. military bases could be maintained in Iraq with a total of 30,000 to 40,000 troops for a long period of time -- maybe a few decades, the radio said.

    The bases will be located at various strategic locations and will serve as air landing strips, for instance, it said, adding that the bases will be sealed and the U.S. forces wouldn't be on patrols as they are now.

    Some U.S. military experts said maintaining a troop presence in Iraq would allow the military to continue training Iraqi forces.

    It would also help discourage other countries, like Iran and Turkey, from entering Iraq, they added.

    Iraq has been gripped by violence since the U.S. led invasion in 2003 and its government has been making slow progress in calming the country.

    The Bush administration has been under increasing domestic pressure from the opposition Democrats and the public, who blame the president for starting the war at the cost of a large sum of money and the U.S.'s international image.

    The Democrats are also demanding that the government phases out U.S. involvement in Iraq.