Washington ? U.S. authorities say they have uncovered an al-Qaida plot to crash an explosives-laden small aircraft into the American consulate in Karachi, Pakistan. That prompted the Homeland Security Department to warn about possible attacks in the United States.

A department advisory said al-Qaida was in the late stages of planning an attack on the consulate using a small fixed-wing aircraft or helicopter.

Such a plot, along with one uncovered last year in which al-Qaida hoped to fly a small plane into a U.S. warship in the Persian Gulf, demonstrated a “fixation” on using aircraft in attacks, the advisory said.

The warning was issued Thursday to U.S. pilots and airport managers as part of a broader bulletin urging vigilance to guard against similar attacks in America.

A U.S. law enforcement official, speaking on condition of anonymity, said a plot against the consulate was uncovered with the arrests earlier this week in Karachi of Waleed bin Attash and five other alleged al-Qaida members. About 300 pounds of explosives and a cache of weapons were seized.

Attash is believed to have played a leading role in planning for the Sept. 11 attacks and the bombing of the USS Cole in Yemen.

Homeland Security officials say there is no specific evidence about an attack using small aircraft in the United States. But the advisory says al-Qaida could try to use such planes because they are easily available and require less pilot skill than large jets.

Security procedures also are less rigorous for small aircraft, there would be no need to attempt to control a large group of passengers and a credit card could be used to rent such a plane, the advisory said.

Pilots and airport officials and workers were urged to be extra alert for suspicious people and activity, aircraft with unusual modifications or people loading unusual cargo onto an aircraft. Vigilance should also be maintained in checking identification, verifying baggage and cargo and watching for “persons who appear to be under stress or under the control of other persons.”

The Aircraft Owners and Pilots Assn., which represents general aviation interests, issued a statement Friday saying it supports greater vigilance but questioning “the sweeping generalizations in this DHS advisory that aren’t necessarily accurate,” said Phil Boyer, the group’s president.

Boyer took issue with a section of the advisory saying that a small plane loaded with explosives could do as much damage as a medium-sized truck bomb. Such a plane, he said, could carry only a few hundred pounds. A truck similar to the one used in the 1993 World Trade Center bombing carried 1,500 pounds.