WASHINGTON, May 13 (Xinhua) -- U.S. Defense Secretary Leon Panetta on Sunday hails the beginning of a new phase of security transition in Afghanistan, which will also be the largest one so far.

    Panetta welcomes Afghan President Hamid Karzai's earlier announcement of areas that have been selected for the next phase of security transition in the country, saying it marks "another significant step" and shows "another tangible sign of progress in our strategy", according to a statement released by Pentagon late Sunday night.

    "With more than 100 districts identified, this third phase will be the largest yet," said Panetta, "when implemented, roughly three-fourths of the Afghan people will live in areas undergoing transition to Afghan security lead."

    He stressed that the transition to Afghan security lead is on track to be completed by the end of 2014, thanks to the growing strength of the Afghan National Security Forces, and the efforts taken by U.S. troops and other ISAF partners.

    U.S. President Barack Obama earlier on Sunday also welcomed the security transition that took place in Afghanistan, saying world leaders will demonstrate their support for Afghanistan beyond 2014 in the upcoming NATO summit in Chicago.

    An Afghan presidential spokesman on Sunday said the government of Afghanistan would soon begin the third phase of security transition from NATO-led troops to the national security force, with the Afghan side taking full control of Uruzgan, Kapisa and Parwan provinces and 122 districts throughout the country.