US Secretary of State John Kerry Sunday warned Beijing against setting up an air defence identification zone (ADIZ) over the disputed South China Sea during a visit to Mongolia.

Washington would consider the establishment of such a zone -- which would require civilian aircraft to identify themselves to military controllers -- "a provocative and destabilising act," Kerry told reporters in Ulan Bator.
The remarks came on the eve of a US-China dialogue in Beijing and after a Hong Kong newspaper cited Chinese army sources as saying Beijing was mulling such a zone, similar to one Beijing established over the East China Sea in 2013.
China claims nearly all of the strategically vital sea despite competing claims by several Southeast Asian neighbours, and has pressed its claims by rapidly building artificial islands suitable for military use.
Washington has responded by sending warships close to Chinese claimed reefs, angering Beijing.
Further US actions in the region "will give Beijing a good opportunity to declare an ADIZ in the South China Sea," a Chinese army source told the South China Morning Post newspaper last week.
Kerry said such a move would "raise tensions".
"We would consider an ADIZ, an ADIZ zone, over portions of the South China Sea as a provocative and destabilising act, which would automatically raise tensions and call into serious question China's commitment to diplomatically manage the territorial disputes of the South China Sea," Kerry said.
"We believe that it is critical that no country move unilaterally to militarise the region," he added.
Kerry also repeated Washington's standard line that it does not take sides in disputes over the sea.
But that stance has been called into question by US Defense Secretary Ashton Carter, who last month accused Beijing of "pressing excessive maritime claims contrary to international law".
China blasted his remarks as expressing "typical US thinking and US hegemony" and a "cold war mentality".
Carter warned a regional security forum in Singapore on Saturday that Chinese construction on an islet claimed by the Philippines would prompt "actions being taken" by the US and other nations.

 Young democracy

The US and Mongolia have enjoyed strong ties for decades. Washington sees the country as a strategic ally against its regional rivals Russia and China.
Mongolia depends on Russia for three-quarters of its oil and China for most of its trade, but sees US relations as a hedge against its neighbours.
Hillary Clinton and US Vice President Joe Biden are among other top officials to have visited the country in recent years as Washington "pivots" to Asia.
Kerry met with Mongolia's President Tsakhiagiin Elbegdorj, and was scheduled to attend a festival of horse-racing and Mongolian wrestling.
"We're delighted to be, in a sense, your third significant friend," Kerry told Mongolia's foreign minister.
"Mongolia has made remarkable progress for a young democracy," he told reporters.
The former Soviet nation of about three million people possesses enormous mineral resources and deposits of gold, copper and uranium, still largely untapped.
Those resources helped the country achieve over 17 percent growth in 2011, but that has since drastically fallen to under 3 percent last year along with plummeting metal prices and capital flight.
Ahead of the visit a US State Department official acknowledged that a US bid for the Tavan Tolgoi coal mine several years ago went to a Chinese contractor.
"We think that the regulatory environment and the legal environment in Mongolia needs to be improved," the official said, after he was asked about transparency in the key sector.