BEIJING (AP) — China's foreign ministry on Friday refused to confirm or deny U.S. Secretary of State Rex Tillerson's assertion that Beijing has threatened to impose unilateral sanctions on North Korea if it conducts further nuclear tests.

Ministry spokesman Geng Shuang reiterated China's support for U.N. sanctions on the North but repeatedly avoided giving a direct answer when asked at a daily press briefing about what other plans China might be considering.

"As for what kind of actions China will take if North Korea conducts another nuclear test, it is a hypothetical question and there is much speculation about that, so I have no comment on it," Geng said.

"China firmly opposes any actions that violate the United Nations Security Council resolutions. This position is quite clear," he said.

Geng also emphasized that China had played an active role in seeking a resolution to the crisis.

"For a long time China has played an important and constructive role on the North Korean issue and made many contributions," he said. "I can say in terms of solving the North Korean crisis, China's efforts can't be overstated."

China wants North Korea to end its nuclear weapons program, but has opposed unilateral sanctions imposed without a U.N. mandate.

Beijing has come under growing U.S. pressure to use its leverage as North Korea's largest trading partner and main source of food and fuel aid to compel Pyongyang to heed U.N. resolutions.

Tillerson said Thursday that Washington knew China was in communication with the regime in Pyongyang.

"They confirmed to us that they had requested the regime conduct no further nuclear test," he said on Fox News Channel.

Tillerson said China also told the U.S. that it had informed North Korea "that if they did conduct further nuclear tests, China would be taking sanctions actions on their own."

Earlier Thursday, the senior U.S. Navy officer overseeing military operations in the Pacific said the crisis with North Korea is at the worst point he's ever seen, but he declined to compare the situation to the Cuban missile crisis decades ago.