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By Erik Ortiz, Courtney Kube and Reuters

Chinese defense officials say they've reached out to the United States to return its underwater military drone it snatched from the South China Sea — a discovery that ratcheted up tensions in a region rife with disputes.

But the ministry warned Saturday that the apparent "hyping up" of the issue by the U.S. was only making matters worse.

In a tweet early Saturday morning, President-elect Donald Trump took aim at the Chinese, accusing them of stealing the unmanned underwater vehicle. He tweeted the same message again a few hours later to correct an earlier misspelling.

"China steals United States Navy research drone in international waters - rips it out of water and takes it to China in unprecedented act," he said in the corrected version.

The drone was grabbed Thursday — the first seizure of its kind in recent memory — about 50 nautical miles northwest of Subic Bay off the Philippines, just as the USNS Bowditch was about to retrieve the device, U.S. officials said.

USNS BowditchU.S. Navy

The Defense Ministry said a Chinese naval vessel discovered a piece of "unidentified equipment" and checked it to prevent any navigational safety issues, before discovering it was a U.S. drone.

"China decided to return it to the U.S. side in an appropriate manner, and China and the U.S. have all along been in communication about it," the ministry said on its website.

"During this process, the U.S. side's unilateral and open hyping up is inappropriate, and is not beneficial to the smooth resolution of this issue. We express regret at this," it added.

Without directly saying whether the drone was operating in waters China considers its own, the ministry said U.S. ships and aircraft have for a long period been carrying out surveillance and surveys in "the presence" of Chinese waters.

Related: Pentagon: Chinese Navy Stole U.S. Underwater Drone

Pentagon spokesman Peter Cook confirmed that the Chinese agreed to hand the drone back after the U.S. "registered our objection to China's unlawful seizure" of the underwater vehicle.

The U.S. had previously said the device was operating lawfully and was collecting oceanic data as part of a routine survey overseen by civilian contractors.

The Pentagon confirmed the incident at a news briefing Friday and viewed China's seizure as serious since it had effectively taken U.S. military property.

"It is ours, and it is clearly marked as ours and we would like it back. And we would like this not to happen again," Pentagon spokesman Jeff Davis said.

Defense officials told NBC News the drone's seizure does not likely qualify as an act of war.

"No one here is freaking out about this, but it was unprofessional," the official said.

The incident follows a series of strained exchanges with China, including over that nation's sharp rebuke of Trump's recent phone call with Taiwan's president — a departure from a decades-long "one China" policy.