China has once again complained a US military flight flew near the South China Sea artificial islands that the country claims is part of its territory.

The Pentagon said on Friday it was looking into the complaint and added that the US regularly conducts training missions with B-52 bomber planes throughout the region.

Navy Commander Bill Urban, a Pentagon spokesman, said there had been no plan to fly a B-52 within 12 nautical miles of any of the three artificial islands.

‘This was not a Freedom of Navigation operation,’ said Urban, referring to regular U.S. Navy missions conducted to challenge what the US believes are excessive territorial claims made by other countries.

‘The Chinese have raised concerns with us about the flight path of a recent training mission. We are looking into the matter.’

The incident involving the B-52 bomber took place last week near the Cuarteron Reef in the Spratly Islands, disputed territory claimed by China and several of its neighbors, the Wall Street Journal said.

China complained the plane flew within 2 nautical miles of the reef, a US defense official said on condition of anonymity.

The official said the United States believed the plane was somewhat farther away but had mistakenly come within 12 nautical miles

China’s defense ministry said in a statement on its website on Saturday that its forces had closely monitored the plane and warned the aircraft to leave.

Referring to the maneuver as ‘provocation’, the ministry said it urged the United States ‘to immediately adopt measures to put an end to such kind of dangerous actions, in order not to impact the two countries’ military relations.’

The US guided missile destroyer USS Lassen sailed within 12 nautical miles of Subi Reef in late October to deliberately challenge China’s territorial claims in the area.

The decision drew an angry rebuke from China, which called it ‘extremely irresponsible.’

USS Lassen was sailing near Subi and Mischief reefs in the Spratly islands, features that were submerged at high tide before China began a massive dredging project to turn them into islands in 2014.

Under the UN Convention on the Law of the Sea, 12-nautical mile limits cannot be set around man-made islands built on previously submerged reefs.

China claims most of the South China Sea, one of the world’s busiest sea lanes, through which more than $5trillion of world trade passes every year.

Source: Reuters