Tillerson also met with British Prime Minister Theresa May and discussed the threat posed to the Mideast region by Iran and the conflict in Syria.
The U.S. pushed for an oil embargo after North Korea conducted its sixth and most powerful nuclear test on September 3. "Russian Federation is the largest employer of North Korean forced labor", Secretary of State Rex Tillerson said in a statement.
But the United Nations has agreed to weaker measures against the North - although the U.N.is banning ban textile exports, an important source of its revenue for the North.
"United Nations Security Council resolutions, including the most recent unanimous sanctions resolution, represent the floor, not the ceiling, of the actions we should take".
UK Foreign Secretary Boris Johnson will meet with US State Secretary Rex Tillerson in London on Thursday for talks that will range from the aftermath of Hurricane Irma to Libya and North Korea, the British Foreign Office has said.
"I think it's clear that with respect to oil and a complete embargo on oil from the U.N. Security Council, that's going to be very hard", Tillerson added, according to an official transcript.
Hurricane Irma: Information on Northeast Florida, Southeast Georgia school schedules
Several schools in our area will be closed on Monday due to the potential of severe weather associated with Hurricane Irma. The county says their government offices will not be open Monday, but will reopen Tuesday at 10 a.m.
The US secretary of state told reporters that Iran was not meeting the expectations laid out in the global nuclear agreement that was reached back in 2015.
Downing Street said Mrs May also raised the Iran nuclear deal - loathed by Donald Trump - "underlining its importance in preventing Iran procuring nuclear weapons". Still he's urging China as a "great country and a world power" to use its leverage as the supplier of virtually all North Korea's oil.
"That is a very powerful tool that has been used in the past, and we hope that China will not reject that", Tillerson said.
South Korea conducted its own missile exercise as Pyongyang fired its missile, taking into account the distance to North Korea's firing site, according to NBC News.
Mr Johnson and Mr Tillerson were joined by colleagues from Italy, Egypt, the United Arab Emirates and France for a meeting on Libya - a "front line in our common struggle against terrorism and illegal migration".