Nine people, including two police officers, were hurt when the king's supporters were attacked by members of the Youth Communist League, police say.

The unrest followed an opposition rally near the palace, where the king is holding three days of celebrations.

Government ministers and foreign diplomats have boycotted ceremonies marking the occasion.

King Gyanendra took the throne in 2001 after a palace massacre, when the then crown prince is reported to have killed his parents, most members of the royal family and himself.

In 2005 he sacked the government and took absolute power, but last year was forced to hand power back to political parties after a wave of pro-democracy street protests.

The republican Youth Communist League has accused the king and his supporters of exploiting the celebrations to try to become politically active again.

Many foreign dignitaries, including those from India, the US and the EU, will not attend the birthday receptions.

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The king's birthday marks a personal milestone for Nepal's ruling Shah dynasty - never before in the 240-year history of the royal family has a reigning monarch lived to the age of 60.

But many of Nepal's new political leaders, including the former Maoist rebels, now want the monarchy abolished.