JOHANNESBURG, May 13 (Reuters) - The leader of Zimbabwe's main opposition group said on Tuesday he would contest a presidential run-off against veteran President Robert Mugabe even if only regional observers could be present.

Morgan Tsvangirai had previously called for unfettered access for international observers, which the government rejected.

"At the moment the obligation is on (regional group) SADC. I am sure that they will fulfil their obligations, especially to send SADC peacekeepers and observers," Movement for Democratic Change leader Tsvangirai told Reuters in a telephone interview. "For us that is sufficient."

Asked how long he was willing to wait for a run-off, after electoral authorities said there would likely be a delay, he said:

"The thing is that the Zimbabwe Electoral Commission, if it has to extend the time of a run-off, it has to do so within a reasonable period. I'm sure that SADC will also be pressurising them to set a date." (Reporting by Caroline Drees; Editing by Matthew Tostevin)