U.S. troops walk from a Chinook helicopter in Uruzgan rovince, Afghanistan July 7, 2017. (REUTERS Photo/Omar Sobhani)

WASHINGTON, July 7 (Xinhua) -- The White House had put limits on the Pentagon's future deployment of extra U.S. troops to Afghanistan despite delegating to U.S. Defense Secretary Jim Mattis the authority to manage troop numbers, according to the Wall Street Journal.

According to the report, the White House sent a classified memo to the Pentagon days after President Donald Trump gave Mattis unilateral authority to set new U.S. troop levels in Afghanistan last month, stipulating that Mattis could send no more than 3,900 extra U.S. troops to Afghanistan without conferring with the White House.

Mattis said in mid-June that he would soon present to the White House a new Afghanistan strategy, including setting new troop levels.

Former U.S. President Barack Obama had planned to reduce the current number of 9,800 U.S. troops in Afghanistan to some 5,500 by the end of 2015 and withdraw all troops by the end of 2016 when his presidency came to an end.

However, given the deteriorating security situation in Afghanistan, the Obama administration repeatedly postponed the withdrawal.

Currently, there are about 8,400 U.S. troops and another 5,000 forces of the North Atlantic Treaty Organization (NATO) on the ground in Afghanistan to train and assist the Afghan forces against the Taliban, and conduct counter-terrorism missions.

The prospect of new U.S. troop levels in Afghanistan came at a time when senior U.S. officials warned of dire security situation in Afghanistan.

In a congressional hearing last month, Mattis said that United States is still "not winning" the longest U.S. war in Afghanistan.

U.S. National Intelligence Director Dan Coats also warned in May that the security situation in Afghanistan would most likely deteriorate in the future even if the United States and its allies offer more military aid.