South Korea's arms procurement agency on Monday approved a long-delayed plan to buy four aerial refueling tankers from 2017-19 to extend the operational range of the country's fighter jets.

The Defense Acquisition Program Administration (DAPA) said it will open bidding for the project in February of next year and select a contractor in October in the same year.

The project is estimated to cost over 1 trillion won (US$900 million), and the budget plan needs parliamentary approval to be implemented by the government.

The Airbus Military's MRTTA330 and Boeing's KC-46 are considered as potential candidates for the acquisition, according to officials.

Fighter aircraft can take off with less fuel and heavier payloads than normal with the aim of refueling in midair. Also, refueling allows the aircraft to increase its strike distance.

During times of crisis, aircraft should be able to continue to fly and await strike orders, which eliminates the time needed for a jet to take off and reach its target, officials said.

"Aerial refueling tankers will increase operational hours of fighter jets by one hour, which will allow military aircraft to operate long-distance missions and carry more weapons," the DAPA spokesman Baek Yoon-hyung said.

Seoul has long sought to deploy aerial tankers to refuel fighter jets in midair and help expand their operational range of F-15K and KF-16 combat jets, but the plan has been delayed due to budget constraints. 

Currently, a KF-16 can conduct missions only for 30 minutes over the easternmost islets of Dokdo and 20 minutes above Ieodo, a submerged South Korean rocky outcropping in waters south of Jeju Island.

With air-to-air refueling, F-15K can conduct missions for 90 minutes above Dokdo and 80 minutes above Ieodo, according to the officials.

On Monday, the DAPA also picked Korea Air Lines Co. as a preferred bidder to develop mid-altitude unmanned aerial vehicles (UAVs) to bolster its monitoring capabilities of North Korea's missile and nuclear program.

LIG Nex1 was chosen to develop joint tactical data link and radar systems and Samsung Thales for an electronic optical infrared system, with Uconsystem picked for the ground control system.

The system development will be completed by 2017 with a budget of about 280 billion won, the DAPA said.

The state-funded Agency for Defense Development launched the indigenous drone program in 2006 and made a prototype in May 2010.

But the project was put on ice in early 2011 as it overlapped with Seoul's plan to buy high-altitude UAVs.

As calls grew for reviving the program to enhance South Korea's surveillance of North Korea's military facilities, scientists resumed their research and completed exploratory development at the end of last year.

The medium-altitude, long-endurance drone is designed to fly at an altitude of up to 10 kilometers and its radar can scan as far as 100 kilometers.

South Korea currently operates an indigenous drone called Night Intruder 300, also known as RQ-101, for reconnaissance and search-and-rescue missions. It was developed by Korean Aerospace Industries in the 1990s and began operation in 2002. (Yonhap News)