Sunday's polls, in which voters elected candidates for about half the Senate's 150 seats, came just three days after Thaksin's dramatic homecoming after nearly 18 months in self-imposed exile following the coup that ousted him.

Voters chose 76 senators, one for each of the country's provinces, but the other 74 seats were appointed by a commission set up under a military-backed Constitution last year.

Among the elected senators, 18 were either ex-MPs or the relatives of top politicians. Most have had links with Thaksin or parties that support him, according to a review of the results.

The activist was instrumental in orchestrating legal challenges to Thaksin's drive to privatise state enterprises, and was a senator in the chamber dissolved by the military after the September 2006 coup.

Royalist generals toppled Thaksin in the military takeover, but his allies swept back to power in elections late last year.

Prime Minister Samak Sundaravej has sharply criticised the Senate selection process as undemocratic, and has vowed to amend the Constitution so that all senators will be elected.

The provision making the Senate only partially elected was one of the most contentious clauses in the new Constitution.

Analysts view the appointed seats as a way for the generals and Thailand's royalist elite to keep their thumbs on the fully elected Lower House, which is dominated by Thaksin's allies.

The Senate must approve all legislation passed by the Lower House. It also plays a watchdog role, with the power to impeach the prime minister and members of Cabinet.

The appointed senators were chosen two weeks ago by a seven-member committee headed by the military- installed chief of the Constitutional Court.

The appointed senators are heavy on retired soldiers and police, as well as lawmakers who served in the Parliament chosen by the military after the coup.

AGENCE FRANCE-PRESSE