Update 11:17 p.m. EDT: China has said U.S. Secretary of State John Kerry did not refer to "provocative" actions by Beijing in the South China Sea while holding a telephone conversation with Chinese Foreign Minister Wang Yi.

"In fact, U.S. Secretary of State Kerry made no such comments during the phone conversation," China Foreign Ministry spokesman Hua Chunying told the official Xinhua news agency late on Tuesday, Reuters reported.

Kerry's message during the phone talks was that the United States does not take sides in the South China Sea dispute, and has no intention to make any judgment on the issue of territorial sovereignty, Xinhua said.

Original story:

China has begun reclaiming land around Johnson Reef to build an airstrip in the disputed Spratly Islands of the South China Sea, the Philippine Foreign Ministry said Wednesday morning.

Foreign Ministry spokesman Charles Jose told Reuters the Chinese had been moving earth and materials to Johnson Reef over recent weeks and was reclaiming land in violation of the Declaration on the Conduct of Parties in the South China Sea, an informal code of conduct for the region.

The ministry had already lodged a protest with the Chinese and raised the issue behind closed doors at last weekend's summit of the Association of South East Asian Nations in Myanmar, Jose said.

The Chinese have been shipping large quantities of soil to the Philippine-claimed reef, apparently in a move to enlarge the land area for security facilities, Philippine and U.S. military sources said Tuesday. China has been building permanent structures in the Johnson Reef, known in the Philippines as the Mabini Reef, since 2012, they told Japan’s Kyodo News.

"There's an ongoing construction by the Chinese according to our intelligence reports," one Philippine military source told Kyodo, saying the Chinese apparently plan to turn the reef into a military outpost.

Kyodo News obtained three pictures of the construction purportedly being undertaken by the Chinese military.

On Monday, meanwhile, the Chinese Foreign Ministry said Vietnam's efforts to muster support over another territorial dispute in the South China Sea would fail, a day after Southeast Asian leaders meeting for a regional summit in Myanmar refrained from criticizing Beijing.

Tensions rose in the sea last week after China positioned a giant oil rig in an area also claimed by Vietnam. Each country accused the other of ramming its ships near the disputed Paracel Islands.

"The facts prove that Vietnam is trying to rope in other parties and put pressure on China, (but) will not achieve its aims," Foreign Ministry spokeswoman Hua Chunying told a news conference. "We hope that Vietnam can see the situation clearly, calmly face up to reality, and stop harassing the Chinese operations."

Speaking to fellow ASEAN leaders at a summit on Sunday, Prime Minister Nguyen Tan Dung said Vietnam had acted with "utmost restraint" and used all means of dialogue to request China remove the rig.