Donald Trump's secretary of state pick Rex Tillerson hit out at China Wednesday during his Senate confirmation hearing, warning the US would send a "clear signal" that the Asian giant must abandon its artificial islands in the South China Sea.
"We're going to have to send China a clear signal that, first the island building stops, and second, your access to those islands is also not going to be allowed," Tillerson told a US Senate panel.
Beijing has fuelled regional tensions by turning tiny, ecologically fragile reefs and islets in the strategically vital South China Sea into artificial islands hosting military facilities.
The former ExxonMobil chief said China's building in the disputed waters and its declaration of an air defence identification zone over the Japanese-controlled Senkaku islands in the East China Sea were "illegal actions."
"They are taking territory or control or declaring control of territories that are not rightfully China's."
Beijing asserts a claim to almost the whole of the South China Sea, based on a "nine-dash line" dating to 1940s-era maps.
An international tribunal -- whose jurisdiction Beijing rejected -- ruled last year that there was no legal basis to such claims.
Tillerson added that "building islands and then putting military assets on those island is akin to Russia's taking of Crimea."
His remarks came amid rising tensions between the two countries as Trump has suggested Washington could jettison its decades-old "One China" policy, and the Chinese military has ramped up activities in a show of strength, with its Liaoning aircraft carrier passing through the Taiwan Strait in a show of strength.
Tillerson said the US should affirm to Taipei it will live up to its commitments to Taiwan, which could require the US to intervene militarily if China attacks the island, but added he did not know of any plans to alter the "One China" policy.
In his remarks to the Senate Foreign Relations Committee, he also criticised China for failing to sufficiently help rein in North Korea.
"China has proven a willingness to act with abandon in the pursuit of its own goals which at times has put it in conflict with American interests. We have to deal with what we see, not what we hope," Tillerson said.
"It has not been a reliable partner in using its full influence to curb North Korea," he added. Beijing is a close Pyongyang ally and is seen as critical in helping contain the pariah state's nuclear activities.
But the former oil executive said disagreements with Beijing on some issues should not preclude "productive partnership" on other matters.
Trump's nominee also branded Russia a "danger" during the hearing, signaling that he is prepared to diverge from the president-elect and take a firm line with Moscow.