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 and a handful of North Korean defectors, 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.
Outreach to China
The mass was one of the most anticipated events of the pope's five-day visit to South Korea, during which he reached out to Asian countries such as North Korea and China which have no formal relations with the Vatican.
Inside the cathedral, Francis made a special point of greeting a number of elderly "comfort women" -- Koreans forced to work in Japanese wartime military brothels.
His reunification message was cloaked in a religious context that avoided any overt political statement, with no mention of the repressive level of control exerted by the regime in Pyongyang over all religious activity.
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.
At the very moment Pope Francis landed in South Korea at the start of his visit on Thursday, North Korea carried out a series of short-range rocket launches into the sea off its east coast.
In his first public comments on arriving, the pope had stressed that peace on the divided peninsula could only be achieved through dialogue, "rather than ... displays of force".
The Catholic Church, like any other religion, is only allowed to operate in North Korea under extremely tight restrictions, and within the confines of the state-controlled Korean Catholics Association.
It has no hierarchical links with the Vatican and there are no known Catholic priests or nuns.
A recent report compiled by a UN Commission of Inquiry into human rights in North Korea concluded that practising Christianity outside the state-sanctioned church amounted to a "political crime".
South Korea has a thriving Catholic community, and large crowds followed the pope everywhere, including a gathering of around 800,000 people Saturday for an open-air mass in Seoul.
'Cancer' of despair
In his speeches and sermons, Francis repeatedly returned to the theme of the high human cost of rampant economic development that allows the poor and vulnerable to fall by the wayside.
In a stark message to wealthier Asian nations, he spoke of a "cancer" of despair in ma