BEIJING — Chinese security forces rounded up more government critics ahead of today’s anniversary of the crushing of the 1989 pro-democracy movement centered on Beijing’s Tiananmen Square, adding to an already harsh crackdown on dissent, activists said.

The Foreign Ministry, meanwhile, lashed out at the U.S. government over calls for a full accounting of the military assault on civilians 22 years ago, saying the issue was closed.

Stricter measures against dissidents are routine on the June 4 anniversary, but this year coincide with the most sweeping suppression campaign in many years. Hundreds of activists, lawyers and bloggers have been questioned, detained or simply have disappeared in the four-month campaign that aims to quash even the possibility of a pro-democracy movement forming along the lines of those sweeping the Arab world.

Twenty-two years later, few young Chinese remember the events that marked the last popular challenge to Communist rule in the country. The decades since have seen the economy boom and the Communist Party relinquish much of its day-to-day control over many areas of society while still making no significant moves toward changing the one-party authoritarian political system.

The Chinese government has never fully disclosed what happened when the military crushed the weekslong Tiananmen protests, which it branded a “counterrevolutionary riot.” Hundreds, possibly more, were killed when troops backed with tanks fought their way to the square into central Beijing on the night of June 3-4.