US defence secretary Ashton Carter on Tuesday told Chang Wanquan, his Chinese counterpart, the US would continue to conduct naval operations in the South China Sea, which Beijing considers to be “illegal.

During a meeting that US officials described as “cordial, Gen Chang told Mr Carter that China would defend what it considers to be sovereign territory and had a “bottom line when it came to US missions in the South China Sea.

The sharp differences were aired when the two defence leaders met for the first time on the sidelines of a Southeast Asian summit in Malaysia. Their conversation came a week after a US destroyer sailed within 12 nautical miles of an artificial island in the South China Sea that is claimed by China and where it is constructing an airfield that could have military use.

The US Navy says the mission, which it insists was a “freedom of navigation operation, was not designed to challenge China’s land claims in the South China Sea, where five other countries also contest many of the islands and land features.

The US says it wanted to show that artificial islands such as the reclaimed land at Subi Reef where the USS Lassen sailed do not confer rights to the seas surrounding them.

Behind the sparring over international law is a broader contest between the US and China in the western Pacific. China’s ambitious programme of land reclamation in the South China Sea is one element of a strategy to slowly shift the balance of power in a region that the US Navy has dominated for seven decades.

Describing the 40-minute conversation between the two defence ministers, the senior US official said Mr Carter “reaffirmed that the United States will continue to fly, sail and operate wherever international law allows and had insisted that “the South China Sea would not be an exception.

Gen Chang argued the Chinese build-up in the South China Sea was largely to help other countries in the region, including with humanitarian assistance.

However, he also told Mr Carter that “we need to do things that help us defend our sovereign territory and I need to be very clear to you that there is a bottom line to this, a US official said.

Gen Chang gave no details about what that “bottom line would entail, the US official added.

Earlier in the day, Admiral Harry Harris, head of the US Pacific Command, told an audience in China that the US would continue to conduct “routine operations in the South China Sea, even as he called for closer ties between the American and Chinese militaries.

US naval operations near territory claimed by China were not “a threat to any nation but were designed to defend freedom of navigation in international waters, Adm Harris insisted.

“We are making it clear that?.?.?.?the military will continue to fly, sail and operate whenever and wherever international law allows, he said in a speech at Peking University’s Stanford Center. “The South China Sea is not and will not be an exception.

Although Adm Harris, who earlier this year accused China of trying to create a “great wall of sand in the South China Sea, issued a strong defence of the US operation last week, his remarks in Beijing were relatively restrained. He said it was important for US and Chinese military leaders to have “personal and candid conversations.

The Financial Times Ltd 2015