Milan, Italy ? A small private plane flying in clear skies crashed into Milan’s tallest high-rise Thursday, killing the pilot and at least three people in the building and triggering global fears that terrorists were seeking to repeat the devastation of Sept. 11.

But Italian officials quickly said that the crash appeared to be accidental, and that the pilot was a 68-year-old Italian man who was flying alone not the victim of a suicide hijacking.

Two women look at smoke pouring from the Pirelli skyscraper in downtown Milan, Italy, after a small tourist plane crashed into it. Police said the pilot of the plane had sent out a distress call just before the crash.

Despite the official assurances, mystery continued to shroud the spectacular crash: How did an experienced pilot hit Milan’s best-known contemporary landmark dead-center on a clear day, creating dazed victims and plumes of smoke that were reminiscent of Sept. 11?

When news first broke that the 32-floor Pirelli Building had been set afire by an airplane crash, stock markets around the world fell. President Bush was notified on an emergency basis, the FBI geared up and Italian Prime Minister Silvio Berlusconi cut short a trip to Bulgaria and headed home. Markets recovered in ensuing hours after the Italian government’s reassurances.

Officials of Italy’s National Flight Agency said Thursday night that a preliminary investigation showed that the pilot, Luigi Fasulo, had taken off from Locarno, Switzerland, where he lived. He was about to land his Air Commander single-engine plane at Linate Airport near Milan when he reported difficulty with the landing gear.

Fasulo “disobeyed” air controller appeals to head west and instead flew north over downtown Milan.

Some officials speculated that the pilot suffered a heart attack or other problem while trying to manually lower the landing gear and lost control of the plane. But the account that he “disobeyed” the traffic controllers helped feed speculation that the crash was not an accident.