U.S. National Security Adviser Jake Sullivan and Chinese Foreign Minister Wang Yi met for a second day in Beijing Wednesday, holding talks that touched on topics that included a potential meeting between the two countries’ heads of state and tensions in the South China Sea.

Both sides said the talks were candid, substantive and constructive, with state-run Xinhua news agency quoting Wang as saying the key to keeping China-U.S. relations on the right track lies in the guidance of the two heads of state.

The two discussed planning for a leader-level call in the coming weeks, according to a statement from the White House. Xinhua said the two also discussed a potential meeting between U.S. President Joe Biden and China’s Xi Jinping.

Sullivan and Wang also discussed the importance of military-to-military communications and holding video calls between their military theater commanders “at an appropriate time,” according to the Chinese readout of the meeting.

“The key to the smooth development of China-U.S. interaction lies in treating each other as equals," Wang said, according to Chinese state broadcaster CCTV.

In addition to maintaining peace and stability in the Taiwan Strait, Wang and Sullivan also discussed disputes in the South China Sea, with Wang warning Washington over supporting the Philippines.

“The United States must not use bilateral treaties as an excuse to undermine China's sovereignty and territorial integrity, nor should it support or condone the Philippines' actions of infringement," according to CCTV.

A White House statement said Sullivan expressed “concern about the PRC’s destabilizing actions against lawful Philippine maritime operations in the South China Sea.”

China’s vessels have clashed with several Philippine ships in the South China Sea, unsettling Washington, which has a mutual defense treaty with Manila. On Tuesday, the head of the U.S. Indo-Pacific Command, Admiral Samuel Paparo, said the U.S. military is open to consultations about escorting Philippine ships in the South China Sea.

Other topics discussed at the meeting between the top officials included China's territorial claims to Taiwan and recent U.S. tariffs on Chinese goods.

Wang told Sullivan the United States should stop arming Taiwan and support “peaceful reunification.”

“Taiwan belongs to China,” Wang said, adding that “Taiwan’s independence is the biggest risk to peace and stability in the Taiwan Strait."

China claims democratically ruled Taiwan is part of its territory and says unification is the only option for the island, by force if necessary. Public opinion polling in Taiwan, however, shows little support for unification with its authoritarian neighbor.

According to the Chinese readout, Beijing also voiced its disapproval of tariffs the U.S. has placed on goods, saying Washington should “stop jeopardizing China’s legitimate interests.”

In addition to raising concerns about China’s unfair trade practices and nonmarket economic practices, the White House said, Sullivan stressed that the “United States will continue to take necessary actions to prevent advanced U.S. technologies from being used to undermine our national security, without unduly limiting trade or investment.”

The talks between the top-level officials continue into Thursday and are expected to cover topics on which the countries butt heads, such as trade, the Middle East, Ukraine and the development of chemicals that are potentially used as components of fentanyl.