"Party leader Thaksin Shinawatra may have an ulterior motive if and when he deems it necessary to organise the mass rally," Thepthai said.

On Tuesday, Thaksin instructed his party members to designate some 3,000 supporters per constituency to be ready to travel to the capital at short notice.

Thepthai said Thaksin's planned move did not bode well for the call for reconciliation with his opponents.

Suspicion deepened after caretaker Natural Resources and Environment Minister Yongyuth Tiyapairat instructed forest rangers to attend tactical arms training, he said.

The prime minister should quickly decide whether to take a political break after the new election, he said, arguing that his decision to run for a party-list seat had not cleared up the uncertainty.

"As the party leader, it is obvious that Thaksin will be at the top of his party list. But the people want to know whether he will resume the premiership," he said.

Former Mahachon leader Anek Laothamatas voiced concern that Thaksin's campaigning might trigger a violent confrontation with opponents.

"Violence and social discord erupt wherever Thaksin is present," he said. "It is time for him to start thinking about bowing out of politics as a form of showing gratitude for the motherland."

The Thai Rak Thai Party deputy spokesman said his party was not intent on confronting opponents as alleged.

"The plan to mobilise 3,000 core supporters per constituency is meant to defend and promote the ruling party," he said, adding that the mobilisation would help the party stay in touch with constituents.

These supporters will be asked to attend a training programme in Bangkok with expenses paid by the party, he said, dismissing speculations about a mass rally.