UPDATE 2-China unloads U.S. soybean cargo amid public worries about cost of trade war

trade war@

* Public support for cargo wanes amid concerns about cost

* Unloading started on Saturday

* Sinograin confirms will pay extra duties, worth $6 million

* Comes as U.S.-China dispute shows no sign of ending (Adding details throughout)

BEIJING, Aug 13 (Reuters) - A vessel carrying U.S. soybeans was unloading its cargo worth at least $23 million at the Chinese port of Dalian on Monday, becoming one of the first shipments to incur hefty new import duties as the trade row deepens between Beijing and Washington.

The docking of the vessel after five weeks anchored off China's coast ended long-running speculation over the fate of the cargo, which had captured public attention.

China's state grains stockpiler Sinograin confirmed in a fax to Reuters it will pay the additional 25 percent import tariff on its 70,000 tonne cargo of the oilseed. That equates to about $6 million.

Comments on the country's Twitter-like Weibo showed early public support for the cargo had started to wane amid concerns that the public is footing the bill for the prolonged trade war.

"Isn't Sinograin state-owned? Who is this tariff hurting? Eventually it is us paying the tariffs and it's us being sanctioned!" said one user.

Two posts about the ship's arrival in dock and the extra costs generated more than 800 comments, mostly negative.

"Are we imposing sanction on ourselves? Common people will have to pay for that," said another Weibo user.

Peak Pegasus started unloading its cargo on Saturday, a port official said on Monday, more than a month after it arrived off China's coast just hours after Beijing imposed 25 percent import duties on $34 billion worth of U.S. goods, including soybeans.

TRADE DISPUTE

The penalties were in retaliation for moves by Washington as part of a tit-for-tat trade dispute between the world's two largest economies.

Last week, Washington said it would start collecting tariffs on another $16 billion worth of Chinese imports from Aug. 23, as it tries to pressure China to negotiate trade concessions. Beijing has said it will retaliate in kind.

Soybeans, which are used to make cooking oil and animal feed, are the top U.S. agricultural export to China, with the trade worth $12.7 billion in 2017.

In the fax to Reuters, Sinograin said the cargo was delayed by port congestion, although two officials at Dalian port said they hadn't seen major backlogs since June.

Two other ships carrying U.S. soybeans, Star Jennifer and Cemtex Pioneer, have been anchored off China's coast for the past few weeks.

This is unlikely to be the start of a trend while China, the world's top importer, can source alternative supplies from exporters such as Brazil, analysts said. Domestic stockpiles are 8.21 million tonnes, close to their highest on records.

"Peak Pegasus is just an extreme case since it failed to make the deadline. Sinograin had to pay for the lesson," said Tian Hao, analyst from First Futures. "But for other buyers, they have turned to other sources such as Brazil."

(Reporting by Muyu Xu and Josephine Mason Additional reporting by Beijing newsroom Editing by Manolo Serapio Jr. and David Holmes)