The Taiwan question is "at the very core of China's core interests" and is "the very foundation of the political foundation of China-US relations", Foreign Ministry spokesman Lin Jian said on Thursday, urging Washington to honor its commitments ahead of a reportedly upcoming summit between the heads of state of China and the United States.

Lin made the remarks at a regular news briefing in Beijing when asked to comment on speculation that Taiwan will be China's top concern during US President Donald Trump's scheduled visit to Beijing.

Lin said that abiding by the one-China principle and the three China-US joint communiques, and honoring commitments made by successive US administrations on the Taiwan question, are international obligations that the US must fulfill.

These obligations are also a necessary prerequisite for the stable, sound and sustainable development of China-US relations, he added.

"China has unwavering resolve in safeguarding national unity and territorial integrity," Lin said.

He stressed that "Taiwan independence" separatism is as incompatible with peace across the Taiwan Strait as fire is with water.

"To maintain cross-Strait peace and stability, one must unequivocally oppose 'Taiwan independence' separatism," he said.

Also at Thursday's news briefing, Lin called on Paraguay to stand on the right side of history.

He urged Paraguay to make the right choice of recognizing the one-China principle and sever its so-called "diplomatic ties" with the Taiwan authorities.

The remarks came as Paraguayan President Santiago Pena made a provocative visit to China's Taiwan region with a delegation of business leaders. Pena arrived in Taiwan on Thursday and is expected to stay until Sunday, according to media reports.

Paraguay is the only South American country and one of 12 countries worldwide still maintaining so-called "diplomatic relations" with the Taiwan region.

Lin said that the one-China principle is a basic norm governing international relations and a prevailing consensus in the international community.

He added that a total of 183 countries have established diplomatic relations with China on the basis of the one-China principle.

"We urge the Paraguayan authorities to come to the right side of history as soon as possible, and make the right decision to recognize the one-China principle and sever so-called 'diplomatic ties' with the Taiwan authorities," Lin said.

mojingxi@chinadaily.com.cn