WASHINGTON (AP) — The United States will press China over its forcible repatriation of refugees to North Korea, a U.S. human rights envoy said Monday. He likened the North's vast gulag to that operated by the Soviet Union in the 1930s.

Robert King is among U.S. officials meeting in Washington this week with China's envoy on Korean affairs, Wu Dawei. The Obama administration is looking for Beijing to use its leverage over its North Korean ally to tamp down its provocative behavior and move toward abandoning nuclear weapons.

The prime focus of Washington's policy is on tackling the emerging threat to the U.S. and its allies posed by North Korea's missile and nuclear programs. But King said human rights were also important for U.S. policy.

He described conditions in North Korea as deplorable, and took particular aim at the prison camp system which he said is estimated to hold between 130,000 and 200,000 people. He said it was "outrageous" that many detainees — more than half according to some reports — are imprisoned because of family ties rather than for committing a crime.

"This is something that the last time it was done in the Soviet Union was in the 1930s. The Soviet Union in the 1970s was enlightened in comparison to North Korea," he told reporters.

King is U.S. envoy for North Korean human rights issues but has limited scope to engage directly with Pyongyang and influence conditions there. Since his appointment three-and-a-half years ago, he has only visited once, in 2011, when the U.S. was contemplating providing food aid to the impoverished country.

King cited as progress the U.N. Human Rights Council's decision in March, with U.S. support, to form a commission of inquiry into allegations of grave abuses and crimes against humanity in North Korea. King said that although the three-member commission was unlikely to be able to visit North Korea either, it would elevate legal pressure on Pyongyang.

"We have to continue to press the North Koreans and call attention to what they are doing," King said. "Are we going to have success tomorrow? Probably not. Are we going to succeed some day? Yes, I think we are. But I think we have got to continue to press and push."

Elevating that pressure, however, could sit awkwardly with efforts to win greater Chinese cooperation — notwithstanding Beijing's annoyance with North Korea's latest nuclear test and subsequent belligerent rhetoric that has prompted the U.S. and its allies to step up military readiness and missile defense in the region.

Asked about the flight of refugees from North Korea to China, King said both sides have stepped up border controls, decreasing the numbers fleeing since 2011.

He said there are indications forcible repatriations from China are continuing.

"We continue to press the Chinese on this issue. It's an issue of concern to us" and South Korea, King said.

Human Rights Watch says after new North Korean leader Kim Jong Un took power, the government decreed a shoot-on-sight order to border guards to stop illegal crossings into China. Returnees to North Korea suspected of religious or political activities while in China face lengthy terms of forced labor in re-education centers, it says.

The Chinese envoy Wu was meeting Monday with the lead U.S. envoy on North Korea, Glyn Davies, and has more meetings at the State Department on Tuesday.