China has slammed the United States' arbitrary seizure of an oil tanker off the coast of Venezuela, saying the move is a grave violation of international law.

The US Coast Guard intercepted an oil tanker off the coast of Venezuela in international waters on Saturday, which the White House claimed was "a falsely flagged vessel operating as part of the Venezuelan shadow fleet to traffic stolen oil".

China always opposes illegal and unilateral sanctions that lack a basis in international law and are without authorization from the United Nations Security Council, Foreign Ministry spokesman Lin Jian told Monday's daily news conference.

Beijing also opposes any actions that infringe upon the sovereignty and security of other countries, and rejects all forms of unilateral bullying, he said, adding that Venezuela has the right to pursue independent development and engage in mutually beneficial cooperation with other countries.

China believes that the international community understands and supports Venezuela's position in safeguarding its legitimate rights and interests, Lin said.