With Taliban insurgents controlling large areas of the country, thousands being killed in the fighting and doubts about the success of the US strategy to force peace talks by stepping up air strikes, the credibility of the Western-backed government is at stake.

Several security incidents marred polling on Saturday, with three police killed and at least eight people wounded by explosions in Kabul.

Clashes erupted between the Taliban and the security forces in at least three provinces.

But wider election concerns so far have centred on technical and organisational problems with biometric voter registration equipment, polling stations not opening on time, missing election materials and delays forcing lengthy waits.

"The biggest problem is with the biometric machines, there are some sites where they're not working and a lot of voters have been discouraged and gone home," said Nasibullah Sayedi, a voter in the western city of Herat.

There were similar reports from other centres including the capital Kabul, while in Uruzgan province in central Afghanistan, angry voters tried to break the biometric devices because of the delays.

At least 15 men were arrested over the incident.

The untried biometric technology, aimed at preventing election fraud, was rushed in at the last minute, over the objections of foreign partners who said there was not enough time to set up the system.

The organisational headaches come on top of fears of violence, particularly following the assassination of the police chief of Kandahar on Thursday, which forced authorities to delay the election in the province by a week.

Taliban militants have issued a series of statements telling people not to take part in what they consider a foreign-imposed process and warning election centres may be attacked.

Thousands of police and soldiers have been deployed across the country but already nine candidates have been assassinated and hundreds of people killed and wounded in election-related attacks.

Australian Associated Press