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. Last Updated: 07/27/2016

U.S. Raises Threat Level to First-Ever Red Alert

WASHINGTON -- The U.S. government raised its threat warning to the highest level for commercial flights from Britain early Thursday, in response to a terror plot thwarted in London. Terrorists had targeted United, American and Continental airlines, two U.S. counterterrorism officials said.

The government said it was banning beverages, hair gels and lotions from flights, saying liquids had emerged as a risk from the investigation in Britain.

Multiple flights to several American cities were put on alert, specifically flights by United, American and Continental Airlines, the two counterterrorism officials said. American and United flights were turned into weapons on Sept. 11, 2001, when they were hijacked and crashed.

"We believe that these arrests [in London] have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," U.S. Homeland Security Secretary Michael Chertoff said.

It is the first time the red alert level, defined as designating a "severe risk of terrorist attacks," has been invoked in the U.S. Homeland Security warning system.

In addition to the red alert for flights from Britain, the alert for all flights coming or going from the U.S. was raised to the high, or orange, threat level "to defend further against any remaining threat from this plot," Chertoff said.

Chertoff said in a statement that "currently, there is no indication ... of plotting within the United States."

A U.S. law enforcement official said there had been no arrests in the United States connected to the overseas plot unraveled Wednesday evening.

Authorities believe dozens of people, possibly as many as 50, were involved or connected to the plot, a senior U.S. counterterrorism official said. The plan "had a footprint to al-Qaida back to it," the official said, speaking on condition of anonymity because of the sensitivity of the situation.

The plan involved airline passengers hiding explosives in carry-on luggage. They were not yet sitting on a plane, but were close to traveling, the official said.

Another counterterrorism official said the investigation, which has been ongoing for months, was "very serious," and that U.S. intelligence had been working closely with the British.

It was not believed to be connected, however, to 11 Egyptian students who disappeared in the United States more than a week ago before reaching a Montana college they were supposed to attend. Three have since been found, and the FBI said neither they nor the eight still missing were believed to be a threat.

Authorities have not yet arrested or detained all suspects believed to be involved in the plot, the second official said, also on condition of anonymity.

Chertoff said, given the higher threat levels, U.S. transport authorities would coordinate with federal partners, airport authorities and commercial airlines to intensify existing security requirements.