JAKARTA (Reuters) - U.S. Defense Secretary Jim Mattis said on Monday he would explore deepening defense ties during a visit to Indonesia, a country that appears increasingly ready to assert its sovereignty in the contested South China Sea.

U.S. Secretary of Defense Jim Mattis is greeted by Indonesia's Minister of Foreign Affairs Retno Marsudi at the Foreign Ministry in Jakarta, Indonesia January 22, 2018. REUTERS/Darren Whiteside

Mattis, ahead of talks in Jakarta, raised the possibility of greater maritime cooperation. An aide noted that Indonesia was also considering purchasing Lockheed Martin Corp’s F-16 fighter jets, in a deal that could be worth billions.

“This is a very strategic partnership,” Mattis said, noting Indonesia was the world’s third largest democracy and the most populous Muslim-majority nation. It is also a vast archipelago of over 17,000 islands, with a strategic maritime reach.

“We’re going to continue our efforts to expand maritime cooperation but also support Indonesia as a sort of fulcrum between the Indian Ocean and the Pacific Ocean,” Mattis told reporters traveling with him.

Indonesia has clashed with China over fishing rights around the Natuna Islands, detaining Chinese fishermen and expanding its military presence in the area in recent years.

In July, Indonesia renamed the northern reaches of its exclusive economic zone in the South China Sea as the North Natuna Sea, a move seen as a significant act of resistance to China’s territorial ambitions in the South China Sea.

After Indonesia, Mattis is expected to travel to Vietnam, which has emerged as the most vocal opponent of China’s expansive territorial claims in the South China Sea, where more than $3 trillion in cargo passes every year.

NO BULLYING

The United States and its allies oppose China’s building of artificial islands in the South China Sea and their militarization, given concerns Beijing might use them to deny access to strategic routes vital to commerce.

Mattis, in comments that appeared directed at China, said the United States wanted to make sure that bigger nations did not impose their will on smaller nations.

“Every nation matters and there should not be any bullying or shredding of trust toward others,” he said.

Mattis kicked off his trip by meeting Indonesia’s Foreign Minister Retno Marsudi shortly after landing in Jakarta late on Monday. He was expected to meet other senior Indonesian officials on Tuesday.

Joe Felter, a deputy assistant secretary of defense, noted that the Pentagon had recently singled out China in a strategy document unveiled last week.

“I think they (the Chinese) have a coherent long-term strategy to exert influence, if not dominate the region,” Felter said.

Felter said the United States counted $1.5 billion in foreign military sales to Indonesia since 2013, including Apache helicopters. He said Indonesia had recently taken delivery of the first three of eight Apache helicopters.

The United States was also expected to explore ways to deepen counter-terrorism cooperation with Indonesia, officials said.