President Trump said the US was committed to working toward a diplomatic solution with North Korea over its nuclear and missile programs, but that Washington was prepared to use a "full range" of military options if necessary.
His remarks were made at a joint news conference with South Korean President Moon Jae-in held in at the presidential Blue House in Seoul on the second leg of Trump's five-nation tour of Asia.
"We call on every responsible nation including China and Russia to demand that the North Korean regime end its nuclear weapons and its missile programs and live in peace," Trump said.
Trump arrived in South Korea on Tuesday after a visit to Japan, where he met with Prime Minister Shinzo Abe. Foreshadowing the next stop on his trip, the president said "China's out trying very hard to solve the problem with North Korea."
"We hope that Russia likewise will be helpful," he said. "If we get China, we get Russia, we have other countries we want to get, we think that things will happen and they could happen very quickly."