Australian Prime Minister Malcolm Turnbull has called on China to avoid actions in pursuit of territorial claims in Asia that could make conflict with the United States more likely.

Speaking in Washington on Monday ahead of a meeting with President Barack Obama on Tuesday, Turnbull said Chinese President Xi Jinping had spoken of his desire to avoid the so-called Thucydides Trap — an academic theory that sees a risk of rivalry between a rising and an established power turning to conflict.

“If avoiding the Thucydides Trap is a core objective of China’s strategy, as President Xi insists it is, then we would hope that China’s actions will be carefully calculated to make conflict less likely not more,” Turnbull told the Center for Strategic and International studies think tank.

He said China should be seeking to reassure neighbors and build confidence about its intentions.

“The legitimacy of claims to reefs and shoals should be a secondary consideration when that objective is focused on,” Turnbull said, referring to China’s territorial claims in the South China Sea, where Beijing has been building artificial islands to extend its reach.

Turnbull said rival claims should be settled under international law and referred to a case the Philippines has brought in the arbitration court in The Hague over its competing claims with China.

Australia has no claims in the sea but urges all parties “to refrain from further construction on those islands or reefs and to refrain from their militarization,” Turnbull said.

Turnbull, who has a tricky balancing act to maintain between China — Australia’s largest trading partner — and the United States — Canberra’s main security ally — said a strong and enduring U.S. presence was needed in Asia to ensure the region’s unprecedented economic growth continued.

In announcing Turnbull’s visit earlier this month, the White House said Obama and the Australian leader were expected to discuss the Trans-Pacific Partnership trade deal awaiting ratification and the fight against Islamic State militants in Iraq and Syria, in which both countries are engaged.

Turnbull met U.S. Defense Secretary Ash Carter on Monday and the two discussed Iraq and Syria and the need to continue close collaboration on security in the Asia-Pacific, Pentagon Press Secretary Peter Cook said.