TORONTO - The Canadian government said in a statement late on Tuesday it had fired the country's top nuclear watchdog, criticizing her for how she handled the closure of a key reactor which makes medical radioisotopes.

The government dismissed Linda Keen from her post as president of the Canadian Nuclear Safety Commission, and appointed as interim president Michael Binder, an assistant deputy minister in the Department of Industry.

It said a permanent replacement would be found as soon as possible.

"Having reviewed the actions of the president around the extended shutdown of the Atomic Energy of Canada Limited (AECL) Chalk River Nuclear Research Universal reactor, it is clear that the government is not satisfied that she demonstrated the leadership expected," the government said in a statement.

"The extended shutdown of the reactor was threatening to cause a national and international health crisis. The president was aware of the importance of maintaining Canada's and the world's supply of medical isotopes. However, given the growing crisis, she did not demonstrate the leadership expected of the president under the existing legislative provisions of the Nuclear Safety and Control Act to put the commission in a position to address the situation in a timely fashion."

Last month, the ruling Conservatives forced legislation through Parliament to order that the Chalk River reactor be restarted for 120 days. The reactor makes more than two-thirds of the global supply of medical isotopes.

The isotopes, when injected into the body, give off radiation that can be seen by a camera to diagnose cancer, heart disease and other medical conditions.

The law overruled the decision of Keen, who said the move was too risky because some safety back-up systems were not working.

The 50-year-old Chalk River reactor was shut down by operator AECL in November, causing the isotope shortage.

Chalk River produces medical isotopes for Canadian health care company MDS Inc and its MDS Nordion division, which is responsible for about half of world supply.

($1=$1.03 Canadian)