Minutes after hijackers slammed planes into the World Trade Center (search), police alerted airport control towers that they considered it "a criminal act," prompting flight restrictions that quickly spread across the nation, according to newly released transcripts.

The Port Authority on Monday released the final set of transcripts from emergency communications during the Sept. 11 (search) terror attack. The disclosure came four months after the agency released 2,000 pages of documents detailing what was said in thousands of other emergency calls that day.

In the newly disclosed transcripts, a caller from the Port Authority (search) police desk tells Chris McCary, a LaGuardia Airport control tower employee, that "they are considering it a criminal act."

"We believe that, and we are holding all aircraft on the ground," McCary answers. The exchange, at 9:10 a.m., came seven minutes after the second plane struck the twin towers.

In an earlier exchange, at 9:07 a.m., a LaGuardia ground control dispatcher tells pilots waiting to take off: "Nobody is going to be leaving La Guardia right now. Everybody stand by."

The Federal Aviation Administration had just banned all takeoffs for flights going to or through New York airspace. About 15 minutes later, the FAA banned takeoffs of civilian aircraft nationwide.

The first set of transcripts, released Aug. 28, included conversations between the police dispatch desk and workers in the towers, some of whom perished.

The Port Authority, which owns the trade center and operates its own police force, had initially sought to withhold the transcripts, fearing it could traumatize families of those who died.

The transcripts include communications between Port Authority police officers and department employees, along with calls between command centers at the trade center, the airports and several sites in New Jersey.

The Port Authority said the transcripts released Monday were delayed because the tapes were discovered later. They cover calls with employees at LaGuardia Airport.