A tense standoff remains in the Thai capital, Bangkok, after violence between troops and anti-government protesters left one soldier dead, apparently from friendly fire, and 18 others wounded.

Heavily armed soldiers were out in force patrolling the edge of the city's financial district, as Red Shirt anti-government protesters continued their rally, which has paralysed the city centre.

On Wednesday, confrontation between troops and anti-government protesters turned streets into battle zones after troops fired at and over the crowd and threw tear gas at anti-government protesters riding motorbikes down a busy expressway, blocking their efforts to take the protest into the suburbs.

Earlier, Red Shirt representatives delivered a letter to the office of the European Union delegation in Bangkok requesting the EU to send a team of inspectors to prevent the government from dispersing their group, which has remained encamped in a major portion of the capital for several weeks now.

"The EU remains deeply concerned about the state of affairs in Thailand and regrets all casualties," Suvi Seppalainen, press officer of the European Union delegation in Thailand, told the media.

Elsewhere in the capital, Thailand's long-silent Yellow Shirt pro-government activists on Thursday demanded military action against the Red Shirts and an end to "anarchy" in the capital.

The re-emergence of the Yellow Shirts, best known for shutting down Bangkok's airports for a week in 2008, added to the volatility on the streets of the Thai capital.