Secretary of State John Kerry has vowed to engage the Chinese government in “a very serious conversation” over satellite images released this week that show China has placed surface-to-air missiles in the Paracel Islands, a contested territory in the South China Sea.

“There is every evidence, every day that there has been an increase of militarization of one kind or another,” Kerry said Wednesday after having been asked about the new development in the Paracels, calling the matter “of serious concern.” He concluded,

“We have had these conversations with the Chinese and I am confident that over the next days we will have further very serious conversation on this.”

The Chinese government has been developing a number of facilities throughout the South China Sea, most of which it claims as sovereign Chinese territory despite no precedent in international law supporting this claim. The Philippines has taken China to the Permanent Court of Arbitration at The Hague, and the case remains pending there. China has vowed to ignore any verdict handed down by the international court.

While much of its development has occurred on the Spratly Islands, contested by Taiwan and the Philippines, it appears to have now begun developing the Paracel Islands, which Vietnam claims as its own. On Tuesday, Fox News published satellite photos showing the presence of surface-to-air missiles on Woody Island in the Paracel chain. Also this week, The Diplomat published images showing increased construction of artificial islands and expansion of Duncan Island in the same chain. While China has been working on developing in the Paracels for at least a year, the pace of this construction has accelerated significantly.

The Chinese government has responded to international alarm regarding its militarization of the Paracel Islands by calling the reports about it “hype.” Chinese state media outlet Xinhua quotes Foreign Ministry spokesman Hong Lei as stating that the presence of missiles on Woody Island is “nothing new” and the Paracel Islands are not “a disputed area.” Chinese Foreign Minister Wang Yi described the military facilities in the region as “limited and necessary” and “consistent with the right to self-protection that China is entitled to under international law.”

Xinhua has also once again attacked the United States for militarizing the region, despite the recent reports that point to China’s belligerent behavior against its neighbors. “If there were a ranking for destabilizers in the South China Sea, there’s no doubt Washington would top the list,” a Friday Xinhua editorial reads, accusing America of becoming “fixated on the South China Sea since Washington announced a pivot to the Asia-Pacific” and “the primary source of destabilization in the area.”

Its neighbors appear unconvinced. The government of Japan, rather than condemning the United States for speaking out against Chinese expansionism, has begun urging the U.S. Navy to expand its presence in the region. Japan makes no territorial claims in the South China Sea, though it claims the Senkaku Islands in the East China Sea, which China also claims. Nikkei notes that Japan has a major interest in the South China Sea remaining open to international travel, as 80 percent of its imports arrive through the body of water. “Tokyo has asked Washington to make more frequent sail-bys of islands in the area as part of its strategy to ensure freedom of navigation,” the report notes.

The United States has engaged in two freedom of navigation exercises in the South China Sea recently. The USS Lassen passed within 12 nautical miles of the Spratly Islands in October 2015; the USS Curtis Wilbur made a similar voyage through the Paracel Islands in January. China has condemned both.