Boeing and Airbus were among three bidders in South Korea's roughly 1.4 trillion won ($1.38 billion) program to buy four refueling tanker aircraft, two people briefed on the matter said on Monday.

South Korea kicked off the acquisition process in March to increase the range of its airborne operations amid rising tensions in the region and with North Korea.

The bids, due Monday, saw the Boeing 767-based KC-46 pitted against Airbus' A330 Multi Role Tanker Transport (MRTT) and Israel Aerospace Industries Ltd's [ISRAI.UL] entry of an overhauled B767-300ER, the people said.

They declined to be identified as the matter remained confidential. South Korea expects to close the deal by end of this year.

Boeing and Airbus are in a global competition to fill various requirements for refueling planes.

Airbus' A330 MRTT has been selected by six countries including Australia, Saudi Arabia, United Arab Emirates and the United Kingdom, with the latest choice by Singapore for six planes in March, according to the company.

In 2011, the U.S. Air Force chose Boeing's KC-46 to start replacing its fleet of ageing KC-135 tankers, and plans to spend $52 billion to develop and buy 179 of the refueling planes.

Tanker aircrafts are used to refuel fighter jets and other warplanes during flight. South Korea expects the acquisition will boost its fighter jets' airborne operation time by more than an hour.