By Dustin Volz

WASHINGTON (Reuters) - U.S. Assistant Attorney General John Carlin said on Tuesday that Chinese hacking activity appears to have declined since the Chinese government vowed last September to stop supporting the hacking of U.S. trade secrets.

The assertion supports findings released earlier this month from cyber security firm FireEye that breaches attributed to China-based groups had plunged by 90 percent in the past two years.

"Generally, people have seen a change in activity," Carlin said at the Center for Strategic and International Studies think tank in Washington.

But "there is debate about how long lasting" the apparent reduction in activity will be, Carlin said, adding that the private sector and U.S. intelligence officers were likely better positioned to assess hacking trends.

Carlin said that agreements on hacking activity with China and among the Group of 20 nations, both announced last year, were important to developing uniform international cyber norms.

Certain countries, such as North Korea, continue to be a "difficult actor" on cyber issues, he said.

(Reporting by Dustin Volz; Editing by Andrea Ricci and Frances Kerry)