Syrians are to vote on Tuesday in a presidential poll that Bashar al-Assad is all but certain to win, but which the opposition has slammed as a "farce" that will prolong the country's three-year war.

The controversial vote will be Syria's first election in nearly 50 years, with Assad and his father Hafez renewing their mandates in successive referendums.

But the vote excludes regime opponents from running and will only be held in areas under army control.

Assad faces two virtually unknown competitors - Maher al-Hajjad and Hassan al-Nuri - while the head of state is glorified in huge posters and billboards set up across territory under regime control.

Nuri, who studied in the United States and speaks English, told the AFP news agency he expected to come second after Assad.

Both he and Hajjar have only lightly criticized Assad's rule, for fear of being linked to an opposition branded "terrorist" by the regime, focusing instead on corruption and economic policy.

The vote takes place as the war continues, with the air force bombarding rebel areas in Aleppo and fierce fighting in Hama, Damascus, Idlib and Daraa.

More than 15 million Syrians will be able to cast their vote in 11,000 ballot boxes distributed in more than 9,000 offices, which will be open from 7am to 7pm local time.

North Korea, Iran and Russia supervising

Observers from countries allied to the regime - North Korea, Iran and Russia - are to supervise the vote, while a security plan has reportedly been put in place in Syrian cities to prevent possible attacks against voters and polling stations.

Syria's divided rebels, like their Western and Arab backers, are powerless as Assad prepares to renew his grip on power, after a string of advances on the ground, mainly in Homs and near the Lebanese border.

Opposition activists have branded the vote a "blood election", while the country reels from a war that has killed more than 162,000 people.

For some time, rumors have swirled that polling stations in Damascus would be targeted by rebels positioned in the nearby countryside.

The Assad regime pulled off a coup last week when thousands of expatriates and refugees living abroad turned out for an early vote in the embassies of their host countries.

More than 95 percent of those registered cast their ballots, the state news agency SANA said.

However, Syrians who entered countries illegally were not allowed to take part and only 200,000 of some three million refugees were on electoral lists abroad.

The Assads have ruled Syria with an iron fist for more than 40 years.

All dissent has been crushed throughout that time, with Assad's father Hafez notoriously crushing a Muslim Brotherhood-led rebellion in Hama in the 1980s, and tens of thousands of people still languishing in jails.

PHOTO CAPTION

A Syrian expatriate living in Yemen holds a ballot paper bearing portraits of Syria's upcoming presidential candidates: (from L-R) Maher al-Hajjar, Hassan al-Nouri and current Syrian President Bashar al-Assad, as they cast their vote in their country's presidential elections at the Syrian embassy in Sanaa on May 28, 2014.

Aljazeera