Thai troops opened fire on rioting anti-government protesters today as the government tried to throw a security cordon around the protest site occupied for nearly two months by the redshirts.

Bangkok's commercial district was turned into a battlefield with troops firing teargas, rubber bullets and live rounds at protesters, who returned fire with stones and homemade rockets on roads surrounding the shopping district.

At least three people have been shot dead in the city in the last 24 hours, and more than 40 wounded.

Reuters reported that a Thai photographer and a foreign journalist had also been shot in yesterday's skirmishes as demonstrators gathered outside the Suan Lum night market to stop soldiers sealing off roads.

A Bangkok-based foreign journalist working for France 24 television station was wounded, the station said, while Reuters said a Thai photographer was also shot.

A renegade general who has been in charge of security for the thousands of protesters is in a stable but critical condition today after being shot in the head last night. It remains unclear who was responsible for the shooting.

Khattiya Sawasdipol, a suspended army specialist better known as Seh Daeng (Commander Red), underwent brain surgery after being hit, apparently by a sniper, while talking to reporters yesterday evening.

The protesters were forced to retreat last night, leaving burning vehicles in their wake as soldiers took control of an intersection leading to a road lined with evacuated hotels and foreign embassies.

Troops fired rubber bullets into Lumphini park in central Bangkok after gunshots were heard near the protesters' base, Thailand television said.

Although soldiers used teargas and water cannon before dawn at the Nana intersection and tackled skirmishes around the city, the demonstrators remained defiant, vowing to fight on to the death.

"They are tightening a noose on us but we will fight to the end, brothers and sisters," a protest leader, Nattawut Saikua, told a cheering crowd of about 10,000 at the main protest site.

Troops have yet to seal all roads leading to the area of luxury hotels and department stores, raising questions as to how soon the government will end the protests.

"An operation to seal off the area has just begun. It will take time. We are doing it in a way that does not cause heavy casualties but tightens the protest area," said a government spokesman, Panitan Wattanayagorn.

The shooting of the general sparked half a dozen confrontations overnight between rock-throwing protesters and armed security forces on the outskirts of the protesters' barricaded encampment.

One protester was shot in the eye and died after a group of redshirts confronted soldiers armed with assault rifles next to a park in the Silom business district, witnesses said. Some protesters hurled rocks and troops fired in return.

This morning, the military brought in armoured vehicles, shut down power in some areas at the protest site and cut some mobile phone services.

Khattiya had been branded a terrorist by the Thai government, which accused him of involvement in dozens of grenade attacks that have wounded more than 100 people.

In recent days he was critical of other redshirt leaders, accusing them of embracing the offers of "national reconciliation" from the prime minister, Abhisit Vejjajiva, which unravelled after protesters refused to leave the streets.

Most businesses and embassies, including the British and US embassies, in the area evacuated staff and closed for the day today. Apartment complexes were mostly empty after the government warned it would shut down power and water supplies, and landlords urged tenants to leave.

The crisis – in which 30 people have been killed since April and more than 1,400 wounded – has paralysed parts of Bangkok and sparked Thailand's deadliest political violence in 18 years, decimating tourism and pushing away foreign portfolio investors.

The latest violence followed tough security measures imposed last night to reclaim Bangkok's commercial district after the collapse of the reconciliation plan proposed last week by Abhisit.

The prime minister is under pressure to end the protests, which began with festive rallies on 12 March and descended into violence that is stoking concerns over the outlook of south-east Asia's second-biggest economy.

The flare-up in violence sent ripples through financial markets and prompted investors to buy government bonds, considered a safe-haven asset, and sell stocks. The yield on five-year government bonds, which moves inversely to the price, dropped to a nine-month low. Stocks fell 1.2%.