An image released by the Philippine Department of National Defense on Sept. 7, 2016, shows a Chinese coast guard vessel near the disputed Scarborough Shoal in the South China Sea. (Dnd Handout/EPA)

The Philippines released photos Wednesday purporting to show Chinese boats near a shoal in the South China Sea, claiming that the presence of new ships in the area could signal another attempt by Beijing to build in disputed fishing grounds.

The outcry could exacerbate tensions during a summit of U.S. and Southeast Asian leaders in Laos over China’s reach into the South China Sea, where Beijing has already constructed artificial islands and other facilities that the West and allies fear could be used as a military foothold in the region.

China claims sovereignty over the sea, which borders the Philippines and several other nations that have challenged Beijing’s push in the area. The United States also has raised concerns about possible Chinese attempts to limit fishing rights and shipping lanes.

In July, the Permanent Court of Arbitration in The Hague ruled against China’s assertion of control over the South China Sea. China has refused to recognize the ruling.

The latest move by the Philippines came two days after its Defense Ministry expressed “grave concern” about a larger-than-normal number of ships in the area, and just hours before U.S., Chinese and Southeast Asian leaders met for the Association of Southeast Asian Nations (ASEAN) summit.

The Permanent Court of Arbitration in The Hague ruled that China does not have historic rights to justify its expansive claims. The verdict, which strongly favored the Philippines, will undermine China's claim to sovereignty under the nine-dash line it draws around most of the sea. (Simon Denyer,Jason Aldag/The Washington Post / Satellite photos courtesy of CSIS)

The pictures from Scarborough Shoal may add a new dimension to an already awkward summit. Before it began, Philippine President Rodrigo Duterte used the Tagalog term for “son of a whore” in railing against President Obama and perceived American interference in Philippine affairs. Obama then canceled a meeting with Duterte.

Scarborough Shoal, a triangular chain of reefs and rocks in rich fishing grounds, lies about 120 miles west of Subic Bay, the site of a former U.S. naval base that American ships, planes and Marines have resumed using in recent years.

So far this week, China has tried to downplay the Philippine claims. Asked Monday about the presence of new Chinese ships, a Foreign Ministry spokeswoman in Beijing said there has been no change in China’s policy or posture and urged reporters not to “hype” the matter.

But observers in Philippines and beyond say it is hard to ignore what could be a move to strengthen China’s presence in the area.

“These pictures are extremely alarming, lending credence to reports by sources in China indicating that Beijing was planning to build facilities in the Scarborough Shoal,” said Richard Javad Heydarian, an assistant professor of political science at Manila’s De La Salle University.

“If China indeed pushes ahead with actual construction, it could lead to collapse in burgeoning negotiations between the Duterte administration and Beijing." 

The Philippine Defense Ministry said the vessels included Chinese coast guard ships, barges that could be used for dredging, and potential “troop carriers.”

But experts said they could not determine from the photos alone what they Chinese ships can do — or why China may have sent them.

“It’s hard to draw any conclusion yet,” said Yanmei Xie, a Beijing-based analyst at the International Crisis Group, "But I'd be skeptical that China would choose to start dredging while the G-20 is ongoing and on the eve of the ASEAN summit."

“It looks like a mixture of coast guard ships and fishing vessels — hardly the precursor of a massive reclamation project,” said Ian Storey, a senior fellow at the ISEAS-Yusof Ishak Institute in Singapore.

But Storey said Duterte could be put in a difficult spot.

“As only America can help the Philippines push back against China and protect its maritime claims, Duterte may well come to regret insulting President Obama," he added.