According to a report published by Bloomberg, 40 percent of the troops have already been recruited in the exercise, which is expected to take two years, the officials said, asking not to be identified so they could discuss sensitive troop movements.
About 13 percent of a fence planned along the 1,456-mile-long border has also been completed, they said.
The Pak-Afghan border has 235 crossing points and it is porous. Some crossing points are used by the militants and drug traffickers, according to the report.
Pakistan has come under increasing pressure to act against the Afghan Taliban and the affiliated Haqqani network since President Donald Trump accused Islamabad of allowing them safe haven.
In January, Trump suspended military aid to the nuclear-armed nation and accused Pakistan of giving “lies and deceit” in return for years of U.S. funding.