An arson attack on the headquarters of one of the two candidates in Egypt's presidential election has marred campaigning for the second round in a vote that has polarised the nation with the choice of an

Islamist or Hosni Mubarak's last prime minister.

Protesters set fire to storage rooms and smashed computers last night at the campaign headquarters of Ahmed Shafiq, a 70-year-old former air force chief and Mubarak official, who was confirmed as a run-off candidate after the first round vote.

His rival is Mohamed Mursi, a senior member of the Muslim Brotherhood, Egypt's main Islamist group which controls the biggest group in parliament after an earlier election. The deciding presidential vote is on June 16th and 17th.

Mr Mursi (60), drew support from a disciplined group of backers of the Brotherhood, banned under Mr Mubarak, and Mr Shafiq attracted Egyptians who want a strongman to restore law, order and prosperity after 15 months of turmoil since the uprising.

Neither won more than a quarter of votes cast in the first round, leaving an agonising choice for a sizeable portion of the electorate who backed more centrist candidates and do not want a conservative Islamist or an ex-military officer at the helm.

Thousands of Egyptians took to the streets last night in protest after the results of the first round were confirmed by the election committee. Some held up posters of Mr Mursi with a cross over his face. But most were chanting against Mr Shafiq.

Dozens then marched from the protests around Tahrir Square, where hundreds of thousands played out a drama that toppled Mr Mubarak, to Mr Shafiq's headquarters in the upscale Cairo district of Dokki. "They seemed to know what they were after and they went directly to the storage rooms and set them on fire using petrol bombs," said Ahmed Abdel Ghani, a member of Shafiq's campaign, surveying a scene of unusable, charred campaign flyers and leaflets scattered on the ground.

The main villa escaped the flames but protesters smashed laptops and computers inside, he said. Daubed on the wall

outside the villa were the words: "No to Shafiq, no to feloul," an Arabic word referring to "remnants" of Mr Mubarak's era.

Mr Shafiq has made no secret of his admiration for the former president, describing him as a role model after his own father.

Protesters threw stones and shoes at him when he voted in Cairo last week.

The flare-up was the latest in an already messy and often bloody transition to democracy since generals took over from Mr Mubarak after a popular uprising forced him in February,

2011. The army has pledged to hand over power by July 1st.

Violence could help Shafiq's cause as his strongest card in the race is his promise swiftly to restore law and order, which collapsed after Mr Mubarak's downfall.Many Egyptians were happy to see the back of Mr Mubarak, yet are now desperate for stability to revive the shattered economy.

Shafiq is seen as having the army backing to achieve that.Both Shafiq and the Brotherhood are now trying to rally support from more centrist voters in the second round. But youth leaders of the uprising fear they would be surrendering their revolution by voting for Mr Mursi or Mr Shafiq and liberals are also deeply uncomfortable with the available candidates.

Liberal and other political groups have often criticised the Brotherhood for being slow to join the anti-Mubarak revolt, acquiescing too quickly to the ruling generals and seeking to dominate the political scene after their parliamentary success.

The Brotherhood denied any role in the attack on Mr Shafiq's headquarters.

Other candidates who lost in the first round also condemned the violence. Hamdeen Sabahy, a leftist candidate who came third in the race and now being courted by the Brotherhood, said in a statement it was the "right of the people to express their opinion provided demonstrations were peaceful".