The public suicide in Paris of Dominique Venner, a 78-year-old right-wing French historian and essayist, has stirred a strong political reaction in the country.

Some 1,500 visitors were cleared out of Notre Dame Cathedral after a man put a letter on the altar of the 850-year-old monument Tuesday, then pulled out a gun and shot himself in the head, three days after a law legalizing same-sex marriage came into effect.

Venner's blog describes his opposition to France's new law authorizing same-sex marriage. In some posts, he criticizes "massive immigration" and what he describes as encroaching Islam; others include historical analysis of revolution or American-European relations.

The suicide was described by National Front leader Marine Le Pen on Twitter as a political act.

"All respect to Dominique Venner whose final, eminently political act was to try to wake up the people of France," Ms Le Pen wrote on Twitter, the BBC said.

"It is in life and hope that France will renew and save itself," the far-right party leader added.

1st suicide in decades at site

In response, Socialist Party chief Harlem Desir said he was shocked by her characterization. He called Venner's death the "gesture of a far-right marginal."

It was the first suicide in decades at the landmark site, Monsignor Patrick Jacquin, the cathedral's rector, told The Associated Press.  

"It's unfortunate, it's dramatic, it's shocking," Jacquin said. The motives for the suicide, and the contents of the man's letter, were unclear.

It says he fought with French forces against Algerian independence fighters a half-century ago in a war that ended with France losing its most prized colony.

Police ushered people out of the cathedral after the shooting, Interior Minister Manuel Valls told reporters from the grand stone plaza in front of Notre Dame. "We call for compassion," he said.

"Notre Dame is the cathedral of Paris, one of the capital's — and the country's — most beautiful monuments, so we realize how symbolic this event truly is."

Opened for evening service

It's highly unusual for the 12th-century cathedral, visited by some 13 million people from around the world every year, to be evacuated, the AP reported.

It opened for an evening service that church officials said would include a prayer for the man who committed suicide and other struggling souls.

After Venner's death, a friend read a message from him on a conservative radio station, Radio Courtoisie, where Venner had once broadcast, the BBC reported.

"I believe it is necessary to sacrifice myself to break with the lethargy that is overwhelming us," he was quoted as saying. "I am killing myself to awaken slumbering consciences."

Venner was once imprisoned for activities with the Secret Army Organization (OAS), which opposed Algerian independence in the early 1960s and tried to assassinate President Charles De Gaulle, the BBC said.

With files from The Associated Press and Reuters