Police in the Nepalese capital, Kathmandu, have used teargas and batons against stone-throwing protesters defying a curfew.
Thousands have defied the curfew in Nepalese cities
Three people have died in two days of unrest, part of widespread anti-government protests.
Both Maoist rebels and opposition political parties have said they will intensify their campaigns.
The protesters want the end of the direct rule imposed by King Gyanendra 15 months ago.
The authorities called a curfew from 1100-1800 (0515-1215 GMT), the third straight day of curfew aimed at halting the protest.
But the shorter curfew hours suggest the government may be nervous about demonstrations, says the BBC's Charles Haviland in Kathmandu.
Several demonstrations took place in and around Kathmandu, despite the curfew.
"People are getting killed anyway. I am not afraid of death," one protester, Ashok Rana, was quoted as saying by Reuters news agency.
"The king has pushed the country into a deep ditch," another protester, Raj Kumar Chhetri, said.
The US urged the king to restore democracy, saying the decision to impose direct rule had failed "in every regard".
US State Department spokesman Sean McCormack said dialogue with political parties was the best way to counter the insurgency.
In an email statement signed by their top two leaders, Prachanda and Baburam Bhattarai, the Maoists said they backed the nationwide strike.
"We... announce we will join the general strike," it said.
Kathmandu saw fierce street battles over the weekend
The rebels said they would take control of the country's roads and destroy all royal statues.
All sign boards saying "His Majesty's Government" would be removed and action would be taken against those paying taxes to the royal government, it added.
Some 13,000 people have died since the Maoist insurgency began in 1996. On Friday attacks left at least five people dead.
The rebels announced a ceasefire in and around the capital, Kathmandu, during the strike.
Home Minister Kamal Thapa told reporters the government had been "restrained even during the curfew".
"We will get stricter now to preserve law and order and keep the situation normal," he said.
Hundreds of opposition figures and activists have been arrested since Friday, according to police officials.
The king took power 14 months ago, accusing political parties of failing to quell a Maoist insurgency.
The seven main political parties said on Sunday they were extending the strike indefinitely.
Three deaths were confirmed at the weekend:
- In Banepa, a town to the east of the capital, one man was shot dead as protesters clashed with police on Sunday
- In Bharatpur, a woman was apparently shot by police on Saturday while sitting on her balcony near the scene of a mass protest
- A man was shot dead on Saturday in the resort town of Pokhara during mass protests.