BEIJING — U.S. Secretary of State John Kerry is in China on a difficult diplomatic mission.

He meets senior Chinese officials Friday in Beijing to seek their help in bringing a belligerent North Korea back to nuclear disarmament talks.

At the same time, he's demanding that China roll back a series of increasingly aggressive steps it has taken to assert itself in territorial disputes with its smaller neighbors.

Kerry faces a tough sell on both counts.

The extent of China's influence with North Korea is unclear following a purge in the isolated country's leadership.

And China has angrily dismissed U.S criticism over its moves in the East and South China seas that have alarmed U.S. allies like Japan and the Philippines.