LONDON — Prime Minister Brown yesterday defended the knighthood of the author Salman Rushdie, despite a warning by Al Qaeda that it is preparing to attack Britain over the award.

“Nothing can justify either threats to the United Kingdom or any form of terrorist activity and it must be the right of the United Kingdom to make its own decisions on all these issues,” he said. His comments came after Osama bin Laden’s number two gave warning that Al Qaeda would strike in retaliation for the award of the honor to the author. Ayman al-Zawahri, the terrorist network’s deputy chief, accused Britain of defying the Muslim world. Mr. Brown rejected Al Qaeda’s threats at a Downing Street press conference alongside Secretary-General Ban of the United Nations, who is on his first official visit to Britain since succeeding Kofi Annan. Earlier, he maintained that Britain would be threatened, “whatever was happening in Afghanistan or Iraq.”

He said the “fight for the future” with extremists had to be fought “not just militarily” but also on a “cultural and ideological” level. In a BBC interview, Mr. Brown said: “You cannot be secure in a situation where you have a set of terrorist groups, loosely linked as Al Qaeda, that are determined to practice carnage across the world, that have struck in many, many countries, have organizations and cells operating right across Europe and in other countries including, of course, Africa as well as in America.”

One of Iran’s most revered Shiite clerics condemned the knighthood as “a very, very vast action against Islam” and said it would give terrorists a pretext to attack Britain. Grand Ayatollah Yusef Saanei told Sky News: “When your Queen awards Salman Rushdie and turns him into a knight, what do you expect? This is a blasphemy. This is an insult to all the prophets of the world. Apart from the fact that this issue insults all the religions of the world, this will also give a pretext to the terrorists. The terrorists can use this as a pretext to do something against [Britain].”

Tessa Jowell, who was culture secretary at the time of the award, said Mr. Rushdie had received it because he was an outstanding writer. “In times when terrorist threats beset the way of life in this country and the way of life in this country is being attacked by terrorists, standing up for free speech and freedom of speech is ever more important ” she said.