SYDNEY (REUTERS) - Tonga should determine its future, not China or any other country, US Deputy Secretary of State Wendy Sherman said during a multi-leg trip to Pacific nations amid growing geopolitical tensions.

At a televised event with university students in the Tonga capital Nuku'alofa on Saturday (Aug 6), Ms Sherman said the United States and Tonga have been fighting alongside each other since World War II, some three decades before establishing formal relations.

She said while the two countries share values of religious freedom and concern for human rights, the US also considers Tonga strategically important.

"Why did the Japanese attack here? Because you were a strategic island that was key to who would rule the Pacific Ocean, who would own this area," she said, invoking the Pacific battle during World War II.

"It is strategic today as well because, as you know, the People's Republic of China wants to be here. They want to invest here," Ms Sherman added.

"What they can't do… is decide your future for you. We want to work with you. We want to partner with you, and we want to make sure you get to choose your own future and that neither we nor anybody else decides it for you," she said.

Top US officials have visited the South Pacific this year as geostrategic competition in the region heightens.

Chinese Foreign Minister Wang Yi visited Samoa and Tonga in May, followed by Australian Foreign Minister Penny Wong in early June.

A day earlier, Ms Sherman met Tonga Prime Minister and Minister of Defence Siaosi Sovaleni, as well as King Tupou VI, marking 50 years of bilateral relations and to discuss establishing a US embassy.

Ms Sherman's tour is scheduled to include World War II commemorations in the Solomon Islands and visits to both Australia and New Zealand.