OTTAWA -- Prime Minister Jean Chrétien called on Canadians to join in a national day of mourning today by participating in memorials for the victims of Tuesday's terrorist attacks.

Mr. Chrétien said he wanted all Canadians to take part in a vigil to be held at noon EDT as a way of showing Canadians' support. He encouraged Canadians in the United States and around the world to take part in ceremonies wherever they are.

"This will show the solidarity that we feel towards our American friends and the families of the Canadian victims," he said yesterday. "We want to fortify their courage in the face of this terrible situation."

U.S. Ambassador Paul Cellucci has been invited to represent Americans in a ceremony on Parliament Hill, while other memorials are planned in several provinces. In Alberta, books of condolence will be signed at the legislature building in Edmonton and a government building in Calgary, to be forwarded to the U.S. consulate, and a moment of silence will be observed at 10 a.m.

In countries around the world, noon vigils were planned in answer to U.S. President George W. Bush's invitation to "share our grief."

Mr. Bush issued a proclamation asking Americans to mark a National Day of Prayer and Remembrance by ringing bells at places of worship at noon and attending candlelight vigils during the evening.

"I encourage employers to permit their workers time off during the lunch hour to attend the noontime services to pray for our land," he said. "I invite the people of the world who share our grief to join us in these solemn observances."

In London, Queen Elizabeth will attend a special service at St. Paul's Cathedral to honour the dead.

In Brussels, officials at the headquarters of the North Atlantic Treaty Organization and the European Union will observe three minutes of silence at noon.

Romano Prodi, president of the EU's executive commission, will stand in silence outdoors in the heart of Brussels' European district with Belgian Prime Minister Guy Verhofstadt, EU foreign policy chief Javier Solana and the president of the European Parliament, Nicole Fontaine.

"In the darkest days of European history, America stood close by us and today we stand close by America," Mr. Prodi said.

In some countries, memorial services have already been held to mark the tragedy.

In Paris, French leaders joined more than 1,000 Christians, Jews and Muslims at the American Church yesterday to mourn the huge loss of life. President Jacques Chirac, Prime Minister Lionel Jospin and cabinet ministers were among mourners who brushed away tears.