The commanding officer of a U.S. Navy destroyer that challenged China's territorial claims in the South China Sea last week spoke for the first time of his ship's encounters with Beijing's navy Thursday.

Cmdr. Robert C. Francis Jr. told reporters that the USS Lassen patrolled with about six or seven miles of Subi Reef in the Spratly Islands, well within the 12-mile territorial limit claimed by China.

Francis said the crew of a Chinese destroyer that shadowed the Lassen for several days contacted the ship with a standard "query" about what the Lassen was doing. Francis said his crew replied that it was operating in international waters in accord with international law.

But the Chinese pressed the matter, he said, by repeating the query over and over.

"All of our interactions were very professional," Francis said. "I never felt threatened." According to Reuters, Francis said the Lassen has had about 50 "interactions" with Chinese military planes and ships on his patrols in the South and East China Seas since May. The commander described that amount of contact as routine.

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"Every day a U.S. ship is down here, we interact with the Chinese," Francis said.

Not all of the interactions are filled with tension. Francis described one encounter with a Chinese vessel that was downright light-hearted.

"[The crew] picked up the phone and just talked to him like, 'Hey, what are you guys doing this Saturday? Oh, we got pizza and wings. What are you guys eating? Oh, we're doing this. Hey, we're planning for Halloween as well'," Francis said. He added that the Chinese sailors responded to their queries in English and talked about themselves, their families and places they've traveled to."

The point of such casual chat, Francis said, was to "show them ... that we're normal sailors, just like them, have families, just like them."

Francis said that as the Chinese destroyer that had been shadowing the Lassen past the artificial islands turned away, "they said, 'Hey, we're not going to be with you anymore. Wish you a pleasant voyage. Hope to see you again.'"

In the United States, much was made of the Lassen patrol, known in the U.S. Navy as a freedom of navigation operation. But Francis said he and his crew saw it as just another day on the seas.

"We enjoyed the extra publicity," he said.

Francis was interviewed on board the USS Theodore Roosevelt, where Defense Secretary Ash Carter and his Malaysian counterpart, Hishammuddin Hussein, watched U.S. Navy fighter jets roar off the aircraft carrier's steel deck.

Carter's visit drew extra attention because of the ship's location, about 150 miles to 200 miles from the Spratlys, and the tensions surrounding China's reclamation work, which Adm. Harry Harris, head of U.S. forces in the Pacific, has likened to building a "great wall of sand" with the potential for confrontations to escalate into armed conflict.

The U.S. contends that under international law the artificial islands built by China are high seas. That means they are not eligible for the 12-nautical-mile zone granted to maritime features such as naturally formed islands capable of sustaining human habitation or economic life.

The Associated Press contributed to this report.

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