Senior election officials in Afghanistan warned that Saturday’s suicide bomb attack outside the Nato headquarters in Kabul threatened to imperil Thursday’s vote if repeated in the coming days.

The bomb attack was launched only hours before a top-level meeting to assess how many polling stations could safely open for voting across the country in the presidential and provincial elections. In the most recent assessment, the number of polling stations has fallen from 7,000 to just above 6,000.

The audacious strike took place in Kabul’s diplomatic enclave in the heart of the city. It was aimed at one of the most high profile international targets – the headquarters of the International Security Assistance Forces (Isaf) – as people reported for work. The blast, the first suicide bomb attack in the capital for eight months, killed an estimated eight people, and injured close to 100. Meanwhile, a British soldier wounded in an explosion on Thursday died in an English hospital, bringing the number of UK military deaths in Afghanistan since the 2001 invasion to 200.

A senior UN official supporting the electoral process called the Kabul attack “a disturbing diversion.”

“This is the first time these attacks have come so close to Independent Election Commission institutions,” he said. “I hope this incident doesn’t distract from the election process.”

The attack has shattered an eerie peace in Kabul which has held in the run up to the election. The calm had led many to believe that Taliban insurgents had decided to allow the election to take place in spite of earlier threats to disrupt it with violence.

One security expert said Saturday’s suicide attack had been well-planned to cast doubt in voters’ minds over security as people prepared to head to the polls.

“The message is: ‘We can strike at will at the centre and, if we can strike there, we can strike at the polling stations’. It’s timed to cause psychological damage, just as much as physical. It’s not too early [in the election process] and not too late.”

He said the attack had also highlighted Kabul’s porous security.

“The driver must have gone through eight or nine checkpoints across the city to get where he was. He was driving a 4x4 and would have been dressed in western clothes. The local security takes one look at a car like that and waves it through.”

The Taliban claimed responsibility for the attack.

“I’m very shocked that people got so close to the front door of Isaf. We go for meetings there all the time,” said Margie Cook, chief elector advisor of the United Nations Development Programme. “I’m hoping it’s a one off event. Kabul has been quiet for month and months. But rather than it happened now than down the road [and on the eve of the election].”

She said tension was building over the competitive nature of the election. It was proving a much tighter race than had been expected with Abdullah Abdullah, a former foreign minister, staging a real challenge to President Hamid Karzai, who has been leading in the polls.

“It’s a much closer contest than people were anticipating,” said Ms Cook. “For a while people thought that it was a fait accompli. Now the level of debate is a signal that the result is not a foregone conclusion.”

One of the latest polls, conducted by the International Republican Institute before July 26, gave Mr Karzai 44 per cent of the vote, Mr Abdullah 26 per cent and Ramazan Bashardost 10 per cent. Ashraf Ghani trailed the leading candidates with 6 per cent.

Many observers are expecting the election to go to a second round that would be conducted on October 1.

On Saturday, Mr Karzai vowed the election would go-ahead in the face of the escalation in violence.

“The enemies of Afghanistan try to create fear among people in this election period but people still realise the importance of going to ballot boxes to cast their votes,” he said in a statement from the presidential palace.”

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