President Barack Obama said Thursday that the United States was trying to “keep a door open” for North Korea to return to multilateral nuclear disarmament negotiations, even as Washington pursues sanctions against Pyongyang. Obama told the Associated Press that the international community could impose even more sanctions on North Korea for its May 25 nuclear test and provocative missile launches, and he said implementation of recent U.N. sanctions on Pyongyang is “going very well.” According to the U.S. president, the only way North Korea is going to improve its dismal economy and join the world community is to abandon its nuclear weapons programs. He said the United States wants Pyongyang “to know that path is still available.” North Korea test-fired four short-range missiles on Thursday.