The United States National Security adviser Robert O’Brien warns China against any attempt to take Taiwan by force, saying maritime landings were notoriously difficult and there was a lot of ambiguity about how the United States would respond.

He was referring to a long-standing U.S. policy of “strategic ambiguity” on the question of whether it would intervene to protect Taiwan, which China considers its province and has vowed to bring under its control, by force if necessary.

Robert O’Brien at an event in the University of Nevada said that China was engaged in a massive naval buildup probably not seen since Germany’s attempt to compete with Britain’s Royal Navy prior to World War One.