Attorney General Eric Holder yesterday called the recent terror plot in the city “one of the most serious in the United States since Sept.11, 2001.”

Authorities said the CIA learned of terror suspect Najibullah Zazi’s ties to senior al Qaeda leaders in August and alerted domestic law-enforcement agencies to the threat.

“There are people both in this country and also abroad who are committed to harming the American people, and they’re actively plotting to do so,” said Holder.