United Nations Secretary-General Ban Ki-moon may not attend the opening ceremony of the Beijing Olympics, joining a growing number of world leaders who are declining invitations to the August event.

"The secretary-general had conveyed to the Chinese government some months ago that he may not be in a position to accept the invitation to attend this important event due to scheduling issues," spokeswoman Marie Okabe said in a news conference on Thursday.

Asked whether Ban would not be attending the Olympics, the spokeswoman said, "Yes, that's correct."

Ban is, however, planning "a substantive visit to China" instead, Okabe said. She declined to give details about what the scheduling conflict was.

Activists have called for leaders to boycott the Summer Games, which run from Aug. 8-24, to protest Beijing's human rights record and reaction to deadly protests in Tibet. Several leaders plan to skip the opening ceremonies.

British Prime Minister Gordon Brown and German Chancellor Angela Merkel have said they are not attending the opening ceremony, while French President Nicolas Sarkozy said he will make a decision closer to the day. A spokesperson for Brown said the prime minister's decision was made earlier and isn't aimed at being a message of protest.

U.S. Democratic presidential candidate hopefuls Barack Obama and Hillary Clinton both called on President George W. Bush to boycott the ceremony.

Prime Minister Stephen Harper said he doesn't plan to attend the ceremony but Canada will not boycott the Olympics.

The European Parliament on Thursday urged European Union countries to consider boycotting the opening ceremony if China doesn't resume talks with the Dalai Lama.

Also on Thursday, the Olympic torch arrived in Argentina for the next leg of the worldwide torch relay. Thousands of police were ready to guard the symbolic flame during its trek through Buenos Aires.

Officials are worried about anti-China protests after torch runs in other cities resulted in scuffles and chaos. Protesters in Buenos Aires warned of "surprise non-violent actions" when the torch is run through the city on Friday.

During the torch relay's last segment in San Francisco, the route was abruptly changed and cut in half to thwart demonstrators.

With files from the Associated Press