By Arshad Mohammed and David Brunnstrom

WASHINGTON (Reuters) - The administration of President Barack Obama is asking other nations to cut the employment of North Korean workers as a way to reduce Pyongyang’s access to foreign currency, a U.S. official said on Thursday.

The official, speaking on condition of anonymity, spoke a day after the United States sanctioned North Korean leader Kim Jong Un for the first time, citing "notorious abuses of human rights" in a move that infuriated the nuclear-armed country.

The effort aims to increase economic pressure on the North, which angered the United States this year by conducting its fourth nuclear test and by carrying out a rocket launch that Washington said used banned ballistic missile technology.

U.S. efforts to revive talks with North Korea on its nuclear program, seen as a threat to U.S. allies Japan and South Korea, have failed to gain traction, prompting U.S. officials to look at additional sanctions to influence its behavior.

The U.S. official declined to name the countries approached about reducing their use of North Korean labor, though he said they did not yet include China and Russia, believed to be among the prime destinations for North Korean workers. It was not clear when the request was made.

The United States said in April it was working to cut off revenue streams to North Korea by targeting remittances from its overseas workers.

China and Russia generally oppose sanctions that do not have U.N. Security Council backing and Beijing especially fears steps that could destabilize its impoverished neighbor.

Asked if the United States was asking other nations to reduce the employment of North Koreans, a U.S. State Department spokeswoman noted that an executive order that Obama signed on March 16 provided tools under which Washington could target such labor.

“The (executive order) includes the authority to target North Korea’s exportation of labor in order to provide Treasury the flexibility to impose sanctions and ratchet up pressure as needed. At this time, we are closely studying the issue,” said Gabrielle Price, spokeswoman for the State Department’s Bureau of East Asian and Pacific Affairs.

A U.N. report last year estimated over 50,000 North Koreans were working abroad, earning the state $1.2 billion to $2.3 billion annually, although some experts question these figures.

Aside from China and Russia, many are believed to be working in African countries and on construction sites in the Middle East, including in Qatar which is preparing to host the 2022 World Cup.

The North Korean government captures the bulk of the foreign exchange earned by its workers abroad, analysts say, but they are allowed to send some back to their families.

The Obama administration carefully weighed its request because of the potential effect on ordinary North Koreans.

"We're talking to them not about termination but about a ramp down," said the U.S. official.

The official said one can make an argument that North Korean workers abroad are treated as "slave laborers" but added that their working conditions abroad might be better than at home.

BURNISHING LEGACY?

North Korea on Thursday reacted angrily to what it described as the United States' "declaration of war" by blacklisting Kim Jong Un for rights abuses, calling the move a "hideous crime," according to the official KCNA news agency.

U.S. officials said they acted in part because of a looming congressional deadline to report on human rights in North Korea.

However, one State Department official described it as in large part an effort by the Obama administration to counter charges that it has been weak on other human rights fronts, including Saudi Arabia, China, Bahrain, Vietnam, and Iraq.

This official said the move was not expected to have any effect on the regime's behavior and was largely "a legacy move" by the Obama White House.

U.S. officials acknowledged that the immediate practical effect of Wednesday's move was likely to be small because North Korean officials such as Kim and the 10 others sanctioned are not believed to have significant assets in the United States.

Peter Harrell, a former State Department sanctions official, said that the drumbeat of sanctions over the past year had likely already driven away any North Korean government money in Western banks.

But he said the sanctions against Kim could help to scare away banks in China or elsewhere that still may handle North Korean transactions. "It does shape business decision-making," he said.

Analysts said North Korea's angry response to the sanctions could preclude future negotiations on the nuclear issue.

However, John Sifton of Human Rights Watch defended targeting Kim, saying talks were dead. "This is an area where the administration is not acting politically or cynically," he said. "They are actually trying to do the right thing."

(Additional reporting by Joel Schectman, John Walcott, Mohammad Zargham and Patricia Zengerle; Writing by Arshad Mohammed; editing by Stuart Grudgings.)