Violence has escalated in Afghanistan with a second day of protests against the burning of Korans by Nato troops, leaving four protester dead and 26 injured.

Up to 1,000 people rallied in the Afghan capital, Kabul, after copies of the Muslim holy booked were burnt at Nato's largest base in Bagram, north of Kabul.

Protests were also organised in the eastern city of Jalalabad.

Twenty-one people, including 11 policemen, were wounded in the capital , Mohammad Zahir, head of Kabul police's crimes unit told Reuters.

There were shootings in both the capital and Jalalabad. It is not clear who was doing the shooting.

One person was killed in Kabul, one in the eastern city of Jalalabad and two in Parwan province.

Demonstrators also set fire to part of the Green Village complex in Kabul, a housing compound where at least 1,500 foreign contractors live and work, Reuters reported.

The US embassy announced its staff were on lockdown and said all travel was suspended.

Afghanistan is a conservative Muslim country where where insult to the religion carries the death penalty.

US commander in Afghanistan, Gen John Allen had issued an apology, admitting that troops had "improperly disposed of a large number of Islamic religious materials which included Korans" but anger refused to die down.

Protesters were heard chanting "Death to America", "Death to Karzai" and blocked the road linking Kabul to Jalalabad, one of the main trade route to the Afghan capital.

Koran Burning Controversy: Thousands of Afghans Protest at Nato Base