Prime Minister Narendra Modi arrived here on Monday on the last leg of his three-nation tour and held a meeting with UN Secretary General Ban Ki-moon, over security and cooperation."Discussed key global issues during the wonderful meeting with UN Secretary General, Ban Ki-moon," Modi tweeted.Anil Wadhwa, external affairs ministry Secretary (East), also tweeted: "We talked about maritime security&cooperation in maritime security".Ban is a South Korean national. He is set to retire in 2016 after two terms. Earlier, Modi held talks with President Park Geun-hye here and the two countries decided to elevate their ties to a special strategic partnership.Both sides agreed to increase their defence and security cooperation and also inked seven agreements, including on avoidance of double taxation and for cooperation between their National Security Councils.