Katmandu, Nepal ? Nepali police fired rubber bullets at thousands of protesters Sunday, struggling to enforce a curfew imposed to keep persistent pro-democracy demonstrators off the streets in the Himalayan country’s deepening crisis.

The protesters were trying to enter the city limits of Katmandu, the capital, when police first fired tear gas, then rubber bullets, independent Kantipur television reported. Doctors at a hospital said they treated three people injured by rubber bullets.

Later, communist rebels attacked security bases and government buildings in Nepal’s mountainous north-central region, officials said today. There was no immediate information on injuries or the extent of damage in the attacks overnight in Chautara, about 75 miles northeast of Katmandu.

Katmandu was under a daylong curfew for the fourth straight day. On Saturday, clashes between security forces and tens of thousands of demonstrators left more than 200 people injured.

The protesters have refused to quit despite King Gyanendra’s offer to allow the alliance of seven opposition parties behind the protests and a general strike to nominate a prime minister and form a government.

Opposition leaders said the king’s offer to resolve a crisis that began after he seized power in February 2005 fell short of a key opposition demand: the return of parliament and creation of a special assembly to write a constitution.

The chaos has stoked worries among the international community of a humanitarian crisis in Nepal, already one of the world’s poorest countries.

Many also worry that a political vacuum could give the Maoist rebels – who have seized control of much of the countryside in a bloody, 10-year insurgency – a route to power.

The opposition called for protests to continue throughout the week, including a massive rally Tuesday along the ring road that skirts the capital.