China has rejected US allegations it is using vague territorial claims to gradually assert control in the disputed South China Sea and in turn accused Washington of exaggerating tensions in the region.

A Chinese foreign ministry spokesman, Hong Lei, said the US should take a “rational and fair attitude”. Hong reiterated China’s position that its claims are based on history and international law, and said some US officials’ remarks were “playing up tensions”.

The United States said on Wednesday that actions by China had raised concerns it was trying to assert control over an area covering roughly 80% of the South China Sea despite the objections of its neighbours.

The resource-rich waters are dotted with reefs and islands subject to multiple disputes involving China, the Philippines, Vietnam, Malaysia, Brunei and Taiwan.

Daniel Russel, the top US diplomat for east Asia, described in congressional testimony actions by China that were raising tensions, including restricting access to a contested reef and imposing fishing regulations in disputed waters.

He said an agreement between China and south-east Asia’s regional bloc, Asean, on a code of conduct to regulate behaviour in the South China Sea was long overdue. China has been reluctant to negotiate with the group as a whole, preferring to deal with nations bilaterally.

Hong said China had been committed to resolving maritime disputes with “directly concerned parties” and attached great importance to implementing a code of conduct with members of Asean.