The unprecedented demand, which has not previously been reported, has elevated tensions over natural resources between the two countries in a volatile area of global strategic and economic importance.

One letter from Chinese diplomats to the Foreign Ministry clearly told Indonesia to halt drilling at a temporary offshore rig because it was taking place in Chinese territory, according to Muhammad Farhan, a member of the House of Representatives Commission I overseeing foreign affairs, which was briefed on the letter.

"Our reply was very firm, that we are not going to stop the drilling because it is our sovereign right," Farhan told Reuters.

A spokesman for the Foreign Ministry said, without elaborating, that any diplomatic communication between states was private in nature and its contents could not be shared.

China's foreign ministry, defense ministry and embassy in Jakarta did not immediately respond to requests for comment.

Three other people, who said they were briefed on the matter, confirmed the existence of the letter. Two of those people said China made repeated demands that Indonesia stop drilling.

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