South Korea and the United States kicked off their largest-ever joint air drill on Friday at a time of elevated military tensions with North Korea.

South Korea and the United States kicked off their largest-ever joint air drill on Friday at a time of elevated military tensions with North Korea.

The so-called "Max Thunder" exercise, which is held twice a year, will last until April 25 and involve 103 aircraft and 1,400 service personnel, a South Korean air force spokesman said.

"In numerical terms, it's the largest exercise of its kind that we've done," the spokesman told AFP.

Seoul's F-15K jet fighters will take part along with US Air Force F-15 and F-16s and US Marines' FA-18 and EA-18 aircraft.

The exercise will focus on "practical scenarios" involving precision attacks on enemy positions and supply-drop missions for troops infiltrating enemy territory, a South Korean air force statement said.

It comes as the allies are winding up separate annual military drills which began late February, and have been denounced by Pyongyang as rehearsals for invasion.

In a pointed protest at the exercises, Pyongyang carried out a series of rocket and missile launches, capped by its first mid-range missile test since 2009 on March 26.