ISLAMABAD, May 1 (Xinhua) -- The Pakistan International Airlines (PIA) has been allowed by the U.S. Department of Transportation to conduct direct flights to the United States with an immediate effect, the airline said on Thursday.

Spokesperson of the PIA Abdullah Hafeez told media that it is the first time that Pakistan's national flag carrier will be operating direct flights to the United States without having any stop on the way.

"Before the 9/11 attacks, the PIA planes did not have the capacity to fly directly to the United States and they had to make stop somewhere. Later on, PIA enhanced its capacity but the U.S. authorities refused to permit PIA for direct flights due to security concerns forcing its flights to have security clearance in Europe," said the spokesperson.

According to the official, under the permission that will expire on April 29, 2021, the PIA would be allowed to operate 12 round-trips or one-way passenger or cargo flights in a month under the condition to inform the U.S. transportation department of the route it took for any passenger or cargo chartered flights.

If a PIA flight heads to the United States from an airport outside Pakistan, it will have to obtain a security clearance, otherwise it would not be allowed to enter the airspace.

Earlier in March this year, a team of the U.S. Transportation Security Administration reportedly visited Pakistan to conduct a final security inspection.

In October 2017, the PIA discontinued its flights to the United States because of increasing operational charges due to stopovers and low business and later started negotiations with the U.S. authorities for the permission of direct flights.