WASHINGTON (Reuters) - The senior U.S. official for North Korea discussed the country with her Chinese counterpart in Tokyo on Thursday, and expressed concerns about the forcible repatriation of North Koreans from China, the U.S. State Department said.

The discussions between Jung Pak and China's Special Representative on Korean Peninsula Affairs Liu Xiaoming followed a visit to Beijing last month by U.S. Secretary of State Antony Blinken, the department said in a statement

Pak noted North Korea's "provocative and irresponsible rhetoric toward its neighbors," and stressed concern about its deepening military cooperation with Russia. She said Russia's veto of a mandate extension for a U.N. panel that monitored North Korea sanctions would hamper efforts to implement U.N. Security Council resolutions, the statement said.

"She also expressed continued U.S. concerns regarding the forcible repatriation of North Koreans, including asylum seekers, to the DPRK and called on Beijing to uphold its non-refoulement obligations," the statement, said, referring to North Korea by the initials of its official name.

The U.N. principle of non-refoulement is supposed to guarantee that "no one should be returned to a country where they would face torture, cruel, inhuman or degrading treatment or punishment and other irreparable harm."

A South Korea-based human rights group reported in December that up to 600 North Koreans had "vanished" after being forcibly deported by China and warned they may face imprisonment, torture, sexual violence and execution in North Korea.

That report by the Transitional Justice Working Group came about two months after South Korea lodged a protest with China over the suspected repatriation of a large number of North Koreans who were trying to flee to South Korea.

Beijing's foreign ministry said in October there were no North Korean "defectors" in China but North Koreans had illegally entered for economic reasons and that China always handled the issue according to the law.

Pak last spoke to Liu in February following a previous Feb. 16 meeting between Blinken and Chinese Foreign Minister Wang Yi in which the U.S. side said the two "affirmed the importance of continued communication on (North Korea) issues at all levels."

Sino-U.S. relations have shown signs of improvement in recent months with steps to re-establish communication channels after ties sank to their lowest levels in decades, but many points of friction remain, including China's close relations with Russia.

In Tokyo, Pak also discussed North Korea with South Korean and Japanese counterparts and underscored the importance of maintaining close trilateral cooperation in addressing the threat it posed, a separate U.S. statement said.

(Reporting by David Brunnstrom; editing by Jonathan Oatis)