NEW YORK (AP) — Tuesday marks the 20th anniversary of the first terrorist attack on the World Trade Center.

A noontime ceremony is planned to honor the six people who died in the 1993 blast in a garage below one of the twin towers. More than 1,000 people were injured.

A moment of silence will be observed at 12:18 — the moment when a truck bomb was detonated.

Six Islamic extremists were convicted of carrying out the bombing, including mastermind Ramzi Yousef.

Police Commissioner Raymond Kelly says the scale of the attack was the first dramatic demonstration that "terrorism is theater and New York is the biggest stage."

The ceremony is being held at the 9/11 memorial that honors more than 2,700 people who died in the 2001 attack at the World Trade Center.