Pope Francis wrapped up the first papal visit to Asia in 15 years on Monday, urging the divided Koreas to reject suspicion and confrontation and unite as "one family, one people".

Pope Francis wrapped up the first papal visit to Asia in 15 years on Monday, urging the divided Koreas to reject suspicion and confrontation and unite as "one family, one people".

The pope's appeal, made at a special inter-Korean reconciliation mass in Seoul, came as South Korea kicked off a military drill with US troops that the North has condemned as a prelude to war.

In his homily to the congregation in Myeongdong cathedral, which included President Park Geun-Hye, Francis said the road to reconciliation was always hindered by unpalatable demands.

"It challenges you, as Christians and Koreans, firmly to reject a mindset shaped by suspicion, confrontation and competition," he said.

Church officials in the South had sent several requests to Pyongyang to send a group of Catholics to attend the mass, but the North declined the offer, citing its anger at Seoul's refusal to cancel the joint military exercise.

"Forgiveness is the door which leads to reconciliation", although it may seem "impossible, impractical and even at times repugnant", Francis said.

"Let us pray then, for the emergence of new opportunities for dialogue, encounter and the resolution of differences ... and for an even greater recognition that all Koreans are brothers and sisters, members of one family, one people," he added.

The mass coincided with the launch of the annual Ulchi Freedom Guardian drill, a largely computer-simulated test of combat readiness for a North Korean invasion involving tens of thousands of South Korean and US troops.

North Korea had repeatedly called for the exercise to be cancelled, and on Sunday its military joint chiefs of staff threatened to "mercilessly open the strongest... pre-emptive strike" if it goes ahead.

The Korean peninsula was divided in 1948 and the split was solidified by the 1950-53 Korean War, which concluded without a peace treaty leaving the two Koreas still technically at war.