Afghan police killed four protestors today in some of the worst violence to erupt over satirical cartoons of the Prophet Mohammed.

Fresh protests erupted in the Middle East, Asia and Africa over the cartoons, which were first published in Denmark in September.

In Iran a crowd pelted the Danish embassy in Tehran with petrol bombs and stones for a second day.

An opinion poll carried out in Denmark suggests that some Danes believe the unrest over the publication of images has heightened the risk of a terrorist attack in the country.

Supermarkets across the Middle East have removed Danish dairy food products from their shelves as a result of the sustained protests.

The move has brought Danish sales to a standstill.

Iran has raised duties on Danish-flagged shipping and is threatening to ban Danish shipping entirely from its ports.

According to the Iranian Commerce Minister, Masoud Mirkazemi, the amount of duties on Danish ships entering Iranian ports will increase from today to become equal to the rate that was effective in 2003. Discounts will also be eliminated.

The latest moves follow an Iranian ban on all Danish imports.

The government in Copenhagen has advised Danes not to travel to Muslim countries because of fears for their safety.

The Danish Foreign Minister, Per Stig Moeller, has offered to visit the Organisation of Islamic States in Saudi Arabia to calm Muslim anger.

Meanwhile, the paper which published the 12 cartoons is exploring a joint declaration with Danish Muslim groups which could reconcile a statement of regret from the paper with a Muslim recognition of Denmark's right of freedom of speech.

Britain and France have expressed solidarity with Denmark in the face of mounting violence.

The UN Secretary-General, Kofi Annan, has expressed his alarm, and has called for restraint.

Two Danish offices closed in Sudan

Elsewhere, the Danish Refugee Council has closed two offices in Sudan after attacks by demonstrators protesting at the publication of the cartoons.

The non-governmental organisation made the decision because Sudanese authorities say they could not guarantee the security of the 15 foreign humanitarian workers and about 60 locals who are employed by the offices.

Olympics security measures discussed

As demonstrations over the cartoons continue, Italian officials have been discussing whether to tighten security measures at the Winter Olympics, which begin in Turin on Friday.

At least 15 heads of state will be at the opening ceremony.

The International Olympic Committee has discussed whether Danish athletes should be granted extra security.