The U.S. Defense Secretary Chuck Hagel hosted the UN Secretary-General Ban Ki-moon at the Pentagon on Thursday, marking the first time that a United Nations secretary-general has visited the Defense Department. \"Secretary Hagel congratulated Secretary-General Ban on his outstanding leadership at the helm of the UN during one of the most turbulent and challenging times in international affairs,\" said a statement released by Pentagon press secretary George Little. The two discussed \"current and potential future UN peacekeeping missions of mutual concern, focusing on the distinctive challenges peacekeepers face in unstable environments,\" Little said. The secretary-general expressed appreciation for the contributions the US has made to peacekeeping, he added. \"The two leaders discussed the heightened tension on the Korean Peninsula and the need for North Korea to live up to its international obligations and commitments as well as the deteriorating security situation in Syria,\" Little said. Ban \"expressed his deepest sympathies and condolences to the American people for those killed and injured in the recent bombings in Boston,\" the statement said. Hagel thanked Ban for his friendship and stated that the Defense Department will strengthen its collaboration with the UN, it said.