ISLAMABAD -- Pakistani voters heeded an opposition call to boycott a referendum Tuesday to decide whether military ruler Pervez Musharraf should remain president for five years, party sources said.

Nazir Dhoki, spokesman for the Pakistan People's Party (PPP) of former prime minister Benazir Bhutto, said voters were staying away in droves.

"Public participation is poor, most polling stations are deserted," he said.

The spokesman said civil servants and teachers from state schools were casting their votes at government buildings in Islamabad but the turnout in residential areas was "not good".

"We are getting similar reports from other cities also," he told AFP.

"People have heeded the boycott appeal."

The government is hoping for a turnout of around 30 percent to legitimize Musharraf's presidency ahead of parliamentary elections scheduled for October.

But opposition political and religious parties have called for a boycott, saying the referendum is an unconstitutional sham designed to perpetuate the military's grip on power following General Musharraf's 1999 coup.

Musharraf made a televised address to the nation late Monday to urge people to vote.

He promised the referendum would be "free, fair and crystal clear" and he would respect the result.

Bhutto told the ***News Daily*** Tuesday that the turnout figure was a key test of grassroots support for Musharraf, who has never sought any kind of mandate from the people to legitimize his military takeover.

"If people boycott the referendum it means that he has lost," she said.