This week, ahead of America’s top defense official’s sit-down with his Chinese counterpart on Thursday, the US sent two B-52 Stratofortress bombers on a flight near contested islands in the South China Sea, in the latest sign of rising tensions.

The aircraft “participated in a routine training mission in the vicinity of the South China Sea,” a statement from the US Air Force said. The flight was part of the US military’s “Continuous Bomber Presence operations,” the statement added, as reported by CNN.

In response to the report, Chinese foreign ministry spokesperson Lu Kang said that China resolutely opposes using the pretext of “freedom of navigation” to disrupt regional peace and stability.

“We will take the necessary measures to protect our sovereignty and security interests,” Lu warned.

Against this backdrop, US Defense Secretary James Mattis met with his Chinese counterpart, Chinese Defense Minister Wei Fenghe, in Singapore on Thursday.

The meeting came after Beijing canceled a high-level military-to-military meeting last month in response to US sanctions placed on Chinese entities for purchasing weapons from Russia.

“Both acknowledged that the meeting itself was significant and that high-level communication can help,” Randal Schriver, a US assistant secretary of defense, was quoted by Reuters as saying. “So I think it was productive in that regard.”

“Two nuclear-armed powers with regional, if not global, interests – we need to make sure that when we step on one another’s toes, it doesn’t escalate into something that would be catastrophic,” Schriver said.