China has deployed anti-aircraft missiles to a disputed island in the South China Sea, according to satellite images and the Taiwan government, increasing tensions just as US President Barack Obama sought regional support to push back against Beijing’s assertive territorial stance.

Taiwan’s ministry of defence said on Wednesday that China had stationed the missiles on Woody island, which is controlled by Beijing but also claimed by Taiwan and Vietnam. The revelations came as Mr Obama concluded a summit with Southeast Asian leaders in which he aimed to corral their support in territorial disputes.

During a September visit to the White House, Chinese President Xi Jinping said Beijing did not intend to militarise the facilities it had built in the South China Sea. However, it was not clear whether he was referring to both the Paracel and Spratly Islands, or just the Spratlys — which China calls the Nansha islands.

The Taiwanese comments confirmed a report by Fox News, which on Tuesday published civilian satellite images showing several mobile missile batteries were deployed on the island, part of the contested Paracel chain, between February 3 and February 14. It said an unnamed US defence official had confirmed the accuracy of the photographs.

Hong Lei, a spokesperson for China’s foreign ministry, told a news conference in Beijing that while he was not aware of the specifics of the matter, the Paracel islands “are China’s inherent territory, and deploying defence facilities on our territory is legitimate and reasonable. The purpose is to enhance our defence capabilities, this has nothing to do with militarisation.”

China and the US have blamed each other for militarising the long-running disputes in the South China Sea, parts or all of which are claimed by China, Taiwan, Vietnam, the Philippines, Malaysia and Brunei.

Beijing’s intensifying programme of reclamation on reefs in the contested waters, and the construction of airfields and other military facilities, has sparked concern in Southeast Asian capitals as well as Washington. The US has responded with so-called freedom of navigation operations, sending military vessels and aircraft near some disputed islands without warning Beijing. The most recent such operation, by a US Navy guided-missile destroyer, came just over a fortnight ago.

Taiwan’s defence ministry said in a statement on Wednesday that it would “watch further developments closely” and called on all parties to “maintain peace and stability together in the South China Sea and avoid adopting any unilateral measures that would increase tensions”.

No one from the Pentagon or the Chinese foreign ministry was immediately available to comment.

The missiles are the latest in a series of steps by Beijing to beef up its military presence on Woody island. Last year China renovated the airstrip, while in October a number of Chinese J-11 fighter planes were briefly based there during exercises. In December China’s state oil company Sinopec announced it would build a large refuelling facility on the island.

“If you put that all together, China is demonstrating that it can harden this into a much more viable strategic outpost,” said Ashley Townshend, an expert on the South China Sea from the US Studies Centre at Sydney University who is a visiting fellow at Fudan University in China. “Beijing is showing how it can increase the cost and risk that it can impose on other countries testing its claims in the region.”

Woody Island is about 300km south-east of China’s Hainan island and north of the disputed Spratly chain, where much of Beijing’s hotly contested reclamation work has been conducted.

News of the missile deployment came after Mr Obama on Tuesday ended the first-ever US-based summit with the leaders of the Association of Southeast Asian Nations, where China’s construction activity in the South China Sea was one of the principal topics of conversation.

The joint statement released after the event called for the maintenance of freedom of navigation and for disputes in the region to be resolved amicably. However, it did not make specific mention of China, a sign of the divisions within the region between China’s allies such as Cambodia and Laos and those locked in simmering disputes with Beijing, including Vietnam and the Philippines.

Speaking on Tuesday, Mr Obama said that the US military would “continue to fly, sail and operate wherever international law allows”. He also said the Asean leaders had “discussed the need for tangible steps in the South China Sea to lower tensions, including a halt to further reclamation, new construction and militarisation of disputed areas”.