The majority of senators have not yet decided if they will back Move Forward Party (MFP) leader Pita Limjaroenrat as prime minister, according to senator Wanchai Sornsiri.

Senators have three options -- vote for Mr Pita, not vote for him or abstain from voting -- but it is hard to say what the majority will decide, and several are not expected to make a decision until voting day, he said.

Mr Wanchai also said he will vote for the prime ministerial candidate nominated by a coalition that manages to secure more than 250 House seats.

The MFP-led bloc, with eight political parties and 313 House seats, needs at least 376 votes in the 750-seat parliament, which comprises 500 MPs and 250 senators, to secure Mr Pita's bid for prime minister.

According to Mr Wanchai, the Senate is unlikely to factor in the allegations made against Mr Pita over his ownership of shares in iTV when they vote, as the issue should be left in the hands of the authorities.

A political activist has asked the Election Commission to investigate Mr Pita, claiming the MFP leader owns 42,000 shares in iTV.