Anti-government protesters have been exchanging fire with army units trying to break up their camp in the centre of the Thai capital, Bangkok.

泰国首都曼谷，反政府武装人员与军队交火，试图突破军队对其进行的封锁。

Troops fired shots and tear gas grenades（手榴弹） , and armoured personnel carriers later breached¹（破坏，违反） the barricades³.

At least four people are reported to have been killed and dozens wounded.

The government says the security operation will be continuing all day.

It insists talks are only possible if the protesters first leave the streets.

"We are still ready to talk. My line is open but protest has to end first," said government advisor⁴ Korbsak Sabhavasau.

The military made loudspeaker announcements on Wednesday morning: "Please leave the site immediately. Officials are about to conduct an operation."

Armoured personnel carriers（装甲运兵车） and soldiers later entered the southern perimeter⁵（周长，周围） of the red-shirt protesters' site, after smashing（粉碎） through makeshift barricades.

"This is D-Day," one soldier was quoted as saying by the Associated Press.

Several thousand people - including women and children - are believed to be inside the camp.

In a separate development, ousted⁶ Thai Prime Minister Thaksin Shinawatra warned that "a military crackdown can spread resentment⁷（愤恨，怨恨） and these resentful people will become guerrillas".

Mr Thaksin was speaking in a telephone interview from an unknown location.

On Tuesday, red-shirt leaders had accepted the offer of fresh talks to be overseen⁸ by senior Senate figures, but they floundered（挣扎，折腾） on the government insistence⁹ that the red-shirts must leave the camp prior to talks.

The two sides have been trading increasingly bitter accusations¹⁰（控告，指责） in recent days.

The government accuses hard-liners within the red camp of using women and children as shields. At a news conference on Tuesday the military showed footage of what it said was a protester holding a baby over a barricade².

The red-shirts, meanwhile, accuse government troops of firing indiscriminately（不加选择地，任意地） on them, although the army said troops were firing live rounds only in self-defence.

About 40 people have been killed in clashes since last week.

The government has decreed（颁布法令） a public holiday until Friday to allow time to resolve the crisis.

The red-shirts have been protesting in Bangkok since 14 March, occupying the shopping district, forcing hotels and shops to close.

The protesters are a loose coalition¹¹ of left-wing activists¹², democracy campaigners and mainly rural supporters of Mr Thaksin, who has lived overseas since he was convicted of conflict of interest.

They are demanding fresh polls because they say the government - which came to power through a parliamentary deal rather than an election - is illegitimate.