U.S. Secretary of State John F. Kerry and Chinese Foreign Minister Wang Yi participate in a joint news conference at the State Department on Tuesday. (Alex Wong/Getty Images)

The two sides of U.S.-China relations were on full display Tuesday, as the top U.S. military officer in the Pacific told Congress that “China is clearly militarizing the South China Sea,” while Secretary of State John F. Kerry, after meeting with his Chinese counterpart, said there is only one U.S. foreign policy in the region and that is to seek a negotiated resolution of the ­issue.

Adm. Harry B. Harris Jr. said that “you have to believe in a flat Earth” to think China’s goal is not to militarize the area and achieve “hegemony in East Asia.” Harris told the Senate Armed Services Committee that he had asked the Pentagon for more overhead surveillance in the disputed South China Sea area.

Kerry, in a news conference with visiting Chinese Foreign Minister Wang Yi, said that the State and Defense departments were “on the same page” but that the Pentagon’s job was to “address what happens if . . . [diplomacy] fails.”

“They have to be prepared for any eventuality,” Kerry said.

The exchanges followed a report this week, based on satellite imagery, that China has installed a series of radar facilities on artificial islands it has built from dredged material on atolls in areas that other countries in the region either claim or say are international waters.

Last week, the administration said that China appeared to have deployed surface-to-air missiles on another artificial island in the disputed sea. A U.S. official on Tuesday night confirmed a report from Fox News that China has deployed fighter jets to the same island.

Harris said that “surface-to-surface, surface-to-air missiles” on one island and “the new radars on the Cuarteron Reef . . . are actions that are changing in my opinion the operation of the landscape in the South China Sea.”

The weaponry “could pose a threat” to U.S. aircraft carriers in the region, he said.

Wang, speaking beside Kerry later in the day, said that “China sees the islands historically as China’s territory” and “has a right to uphold its territorial integrity and lawful and legitimate maritime rights and interests.” At the same time, he said, “we are committed to resolving the disputes through dialogue and negotiations in a peaceful way.”

The United States has called for international arbitration of the regional dispute and sent warships and aircraft to patrol what it says are international waters.

Wang said that the “South China Sea issue is not and should not become an issue between China and the United States” and that it should be resolved directly between the regional parties.

“There have not been any problems with regard to freedom of navigation,” he said, and “no commercial vessel has encountered any problems.” China and the countries of the region, he said, “have the capability to maintain peace and stability in the South China Sea, which we see in our own interests. And we don’t hope to see any more close-up military reconnaissance or the dispatch of missile destroyers or strategic bombers” to the area.

For much of their news conference, both Kerry and Wang hailed what they described as growing U.S.-China cooperation on issues including the Iran nuclear deal, climate change, counterterrorism and ending the civil war in Syria.

“The reason that we’ve been able to cooperate in areas where our interests and our values are aligned, despite the fact that we have clear differences on some other issues, is that both the United States and China are deeply committed to an open and frank dialogue,” Kerry said. “We are two powerful nations, the two largest economies today, and we have an ability therefore to be able to make good things happen when we decide to.”

Both said that the United Nations was close to agreeing on a new resolution against North Korea for its recent nuclear and ballistic missile tests that violated U.N. mandates. Both also called for denuclearization of the Korean Peninsula and a resumption of diplomatic talks with the North.

In addition, Wang pointed out that China is now the largest U.S. trading partner, with bilateral trade last year of $558.4 billion. Although that still puts China slightly behind Canada for the whole of 2015, the Chinese overtook Canada for the last several months of the year.

Simon Denyer in Beijing and David Nakamura in Washington contributed to this report.