VIENTIANE (Reuters) - Southeast Asian nations expressed serious concern on Saturday about growing international tension over disputed waters in the South China Sea.

The artificial island at the southern end of Mischief Reef showing a newly-built seawall on its north side and a completed dock are shown in this Center for Strategic and International Studies (CSIS) Asia Maritime Transparency Initiative January 8, 2016 satellite image released to Reuters on January 15, 2016. REUTERS/CSIS Asia Maritime Transparency Initiative/Digital Globe/Handout via Reuters/Files

China claims most of the sea but Southeast Asian countries Malaysia, the Philippines, Brunei and Vietnam have rival claims. Friction has increased over China’s recent deployment of missiles and fighter jets to the disputed Paracel island chain.

“Ministers remained seriously concerned over recent and ongoing developments,” the 10-members Association of Southeast Asian Countries (ASEAN) said in a statement after a regular meeting of the group’s foreign ministers in Laos.

Land reclamation and escalating activity has increased tensions and could undermine peace, security and stability in the region, ASEAN said in the statement.

The United States has criticized China’s building of artificial islands and facilities in the sea and has sailed warships close to disputed territory to assert the right to freedom of navigation.

On Friday, the United States urged China’s President Xi Jinping to prevent the militarisation of the region.

Vietnam, which accused China of violating its sovereignty with the missile deployment, echoed the U.S. call on Saturday.

“We call for non-militarisation in the South China Sea,” Deputy Prime Minister and Foreign Minister Pham Binh Minh told reporters after meeting his ASEAN colleagues.

“We have serious concerns about that,” he said, when asked about China’s increasing military activity in the region.

The group agreed to seek a meeting between China and ASEAN’s foreign ministers to discuss the South China Sea and other issues, Cambodian Minister Hor Namhong said.

China’s maritime claims are ASEAN’s most contentious issue, as its members struggle to balance mutual support with their growing economic relations with Beijing. China is the biggest trade partner for many ASEAN nations.

Neighbours Vietnam and China compete for influence over landlocked Laos, which has no maritime claims but finds itself in the difficult position of dealing with neighbours at odds over the South China Sea. Laos is tasked with finding common ground on the issue as the ASEAN chair in 2016.

“The South China Sea issue is a headache that Laos would really rather not have to deal with,” said one Western diplomat in Vientiane.

Thongloun Sisoulith, Laos Deputy Prime Minister and Minister of Foreign Affairs, played down the challenge.

“We are a close friend of Vietnam and China, we try to solve the problems in a friendly way,” he told Reuters on Saturday. “We are in the middle, but it’s not a problem.”

Barack Obama is set to become the first U.S. president to visit the country in September to attend an annual summit hosted by the ASEAN chair.