WASHINGTON/BEIJING (Reuters) - The United States expects China to return soon an underwater U.S. drone seized by a Chinese naval vessel last week, with one U.S. official telling Reuters the exchange could happen as early as Tuesday at an agreed location in the South China Sea.

China’s seizure of the unmanned underwater vehicle (UUV) triggered a diplomatic protest and speculation about whether it will strengthen U.S. President-elect Donald Trump’s hand as he seeks a tougher line with Beijing.

A Chinese warship took the drone, which the Pentagon says uses unclassified, commercially available technology to collect oceanographic data, on Thursday about 50 nautical miles northwest of Subic Bay in the Philippines.

The U.S. officials, who spoke on condition of anonymity, said talks with Beijing on the timing of the exchange were advancing, with two saying they expected the incident to be resolved satisfactorily “relatively soon.”

One said the exchange could take place near the disputed Scarborough Shoal in the South China Sea as early as Tuesday, local time. A U.S. destroyer would likely receive the drone, although the mechanics of the exchange were unclear.

Pentagon spokesman Peter Cook at a news briefing said only that “We’re working out the logistical details with Chinese officials”.

In Beijing, China’s foreign ministry said the Chinese and U.S. militaries were having “unimpeded” talks about the return.

The seizure has added to U.S. concerns about China’s growing military presence and aggressive posture in the disputed South China Sea, including its militarization of maritime outposts.

The U.S. Navy has about 130 such underwater drones, made by Teledyne Webb, each weighing about 60 kg (130 pounds) and able to stay underwater for up to five months. They are used to collect unclassified data about oceans, including temperature and depth. They are used around the world, but it is unclear how many are used in the South China Sea.

KEEP THE DRONE!

Trump, who takes office on Jan. 20, waded into the dispute over the weekend, saying in a tweet: “We should tell China that we don’t want the drone they stole back - let them keep it!”

An unmanned underwater vehicle similiar to the one seized by the Chinese Navy. Courtesy Santiago Carrizosa/U.S. Navy

Trump has threatened to declare China a currency manipulator and force changes in U.S.-Chinese trade policy, which he says has led to the greatest theft of American jobs in history.

Trump has also raised questions about the most sensitive part of the U.S.-China relationship: whether Washington would stick to its nearly four-decades-old policy of recognizing that Taiwan is part of “one China.”

Asked about Trump’s comments, Hua said describing the drone as stolen was “completely incorrect”.

“China’s navy had a responsible and professional attitude to identify and ascertain this object,” she said. “If you discover or pick something up from the street you have to examine it and if somebody asks you for it you have to work out if it’s theirs before you can give it back.”

Cook called the seizure illegal and said Washington was using military and diplomatic channels to secure the drone’s return. Pentagon officials have sought to be firm without escalating the incident.

Another senior U.S. official, speaking on condition of anonymity, said the somewhat muted U.S. response to the seizure, coupled with Trump’s abandonment of the Trans-Pacific Partnership trade agreement, Philippine President Rodrigo Duterte’s erratic policies and Malaysia’s corruption scandal, has caused some U.S. allies to worry increasingly about the possibility of a declining American commitment to the region.

The Philippines said it was troubling that the incident took place inside its exclusive economic zone (EEZ), saying it increased the likelihood of “miscalculations that could lead to open confrontation” very near the Philippine mainland.

DEEP SUSPICIONS

China is deeply suspicious of any U.S. military activities in the resource-rich South China Sea, with state media and experts saying the use of the drone was likely part of U.S. surveillance efforts in the disputed waterway.

The overseas edition of the ruling Communist Party’s People’s Daily said in a commentary on Monday the USNS Bowditch, which was fielding the drone and was set to pick it up, was a “serial offender” when it came to spying operations against China.

Ni Lexiong, a naval expert at Shanghai University of Political Science and Law, told Reuters he believed the Chinese navy probably had orders to take the drone.

But Ni said the incident was very different from the 2001 intercept of a U.S. spy plane by a Chinese fighter jet that resulted in a collision that killed the Chinese pilot and forced the American plane to make an emergency landing at a base on Hainan.

“This is a much smaller incident, it won’t affect the overall picture of China-U.S. relations,” he said, adding he did not expect China to seek an apology.

The 24 U.S. air crew members were held for 11 days before being released, souring U.S.-Chinese relations in the early days of President George W. Bush’s first administration.

However, Greg Poling, a South China Sea expert at Washington’s Center for Strategic and International Studies, said the U.S. military could feel compelled to take steps to further assert freedom of navigation in the region.

“For a lot of folks in the Pentagon, this over-stepped that line between legal contestation and a military threat,” he said.

While the U.S. Navy under the Obama administration has sent warships periodically sailing near artificial islands claimed by China over the last year or so, it has mostly acted cautiously, seeking to avoid escalation with Beijing, which claims large swathes of the resource-rich waterway.

In October, the United States carried out a freedom of navigation operation in the South China Sea, sailing within waters claimed by China, but not within the 12-nautical-mile territorial limits of the islands.

Despite Trump’s more aggressive tone, he has given no clear policy on how he plans to deal with the dispute in the South China Sea.