WASHINGTON • The United States naval challenge to China's territorial assertiveness in the South China Sea this week came after months of frustration within the Pentagon at what some defence officials saw as unnecessary delays by the White House and State Department in approving the mission.

As early as mid-May, the Pentagon was considering sending military aircraft and ships to assert the principle of freedom of navigation around China's artificial islands in the Spratly archipelago, after Defence Secretary Ash Carter requested options to respond to their rapid construction.

The Pentagon and US military officials ran into "repeated stalling" from the White House and State Department, said one US defence official, who requested anonymity.

Both wanted to avoid giving the appearance that any operation was in response to other events, the official said, such as the breach of 21 million US personnel records that has been linked to hackers in China.

By late last month, a consensus had been reached to go ahead with the patrol.

US President Barack Obama had to weigh the need to take action against the risks of sparking an armed conflict. But the hold-up subverted the initial intent to make the patrols a routine part of operating in one of the world's busiest sea lanes, the source said.

REUTERS