Nyqvist broke into American movies with his role as a nuclear scientist in "Mission: Impossible Ghost Protocol".

The French foreign ministry refused to say whether it had information about possible preparations by for a chemical attack.

In season 3, the series pulled in average 3.7 million total viewers, including 1.9 million among adults 25-54 and 1.7 million adults.

"The number you have right now is 27, (it) may increase significantly once we are able to validate all this information," a spokesman said.

The Metropolitan Transportation Authority, which manages the city's aging public transit system, said the situation was under investigation.