Former Appeals Court chief Prasopsuk Boondech was among four senators vying to become speaker of the 150-member upper house that is meant to act as a check on the pro-Thaksin government elected in December after a 2006 coup.

Under the 2007 army-designed constitution which replaced the 1997 'People's Charter', the new Senate consists of 76 elected members and 74 appointed by top civil servants.

It can pass laws, appoint independent watchdog bodies and recall cabinet ministers, top legislators and judges accused of corruption.

Pro-Thaksin senators had backed Taweesak Kidbanjong, a former provincial governor from the northeast, MR Thaksin's heartland, for the speaker's post.

'The fact that MR Prasopsuk won the vote instead of other candidates known to be close to politicians in the government is a good start for the integrity of this Senate,' television commentator and former senator Chirmsak Pinthong said.

'We will have to see if money or vested interests will change some of these senators eventually,' he said.

Mr Thaksin was ousted in a bloodless coup by generals who accused him of presiding over rampant corruption and undermining independent watchdogs - charges he has denied.

Earlier this week Mr Thaksin pleaded not guilty to charges that he and his wife violated anti-graft laws that prevent serving politicians and their spouses from doing business deals with state agencies.

Mr Thaksin's opponents, who led street protests agains him prior to the coup, have accused the new government of trying to interfere in the judicial system to get him off.

The People's Alliance for Democacy said it would stage a demonstration in Bangkok on March 28 to expose such alleged attempts by 'Thaksin's nominee government'. -- REUTERS