Singapore's prime minister visited Australia on Wednesday to upgrade a free-trade agreement and to finalize a deal that will double the capacity of Singaporean military training facilities in the Australian tropics.

Singaporean Prime Minister Lee Hsien Loong told the Australian Parliament that China was the biggest trading partner of both nations, which were also allies of the United States.

"We both see the United States as a benign force playing a major role in fostering peace and stability in Asia," Lees said.

Australian Prime Minister Malcolm Turnbull said both countries shared a common strategic outlook. He made an apparent veiled criticism of China's increasingly aggressive territorial claims in the South China Sea and its refusal to abide by international law to resolve competing claims.

"Singapore and Australia are at one in defending the rule of law and rejecting the proposition that might is right," Turnbull told Parliament.

Australia announced in May that Singapore will spend up to 2.25 billion Australian dollars ($1.7 billion) to double the capacity of its facilities in military training areas in Queensland state. That would allow up to 14,000 Singaporean troops to train in Australia for up to 18 weeks a year.

"Our decision to grant Singapore the special level of access underlies the enormous trust and respect that exists between our respective armed forces," Turnbull said. "It also reflects our commitment to do more as security partners, especially as our strategic circumstances change."

Australia and the United States last week struck a cost-sharing deal to pay for more than AU$2 billion in infrastructure needed to be built near the northern city of Darwin to accommodate up to 2,500 U.S. Marines.

The number of Marines rotating through the Darwin training hub has grown since the first contingent of 200 visited for six months in 2012.

Australia was the first country to establish diplomatic ties with Singapore when the city-state became independent in 1965 and the countries have longstanding defense and commercial ties.

Their bilateral free-trade deal was signed in 2003.