FILE PHOTO: U.S. Special Representative for North Korea Policy Joseph Yun answers questions from reporters following meeting with Japan and South Korea chief nuclear negotiators to talk about North Korean issues at the Iikuraguest house in Tokyo, Japan April 25, 2017. REUTERS/Toru Yamanaka/Pool

WASHINGTON (Reuters) - The United States has been engaging in back-channel diplomacy with North Korea for several months, the Associated Press reported on Friday, as President Donald Trump stepped up his warnings to Pyongyang amid rising tensions in the region.

The dialogue involved Joseph Yun, the U.S. envoy for North Korea policy, and Pak Song Il, a senior North Korean diplomat at the United Nations, the AP reported, citing unidentified U.S. officials and others briefed on the process.