Thailand’s Pheu Thai party says it has the support of six more parties in its attempt to form a government – still short of the required backing – as the country remains in political deadlock almost three months after an election.

Thailand has been under a caretaker government for 142 days and faces prolonged uncertainty after election winners Move Forward was blocked from forming a government by conservative legislators allied with the royalist military.

Second-place Pheu Thai, a political heavyweight that was driven from power in coups in 2006 and 2014, withdrew its backing for Move Forward last week but faces an uphill battle to win support from a parliament over which the military commands significant influence.

“Pheu Thai hopes to ease political factionalisation and gain support from all members of parliament, political parties and senators,” Pheu Thai leader Chonlanan Srikaew told a news conference on Wednesday.

The announcement comes after the populist Pheu Thai won support from third-place Bhumjaithai, which had refused to back Move Forward over its controversial plan to amend a law that insulates the monarchy from criticism.

Pheu Thai, founded by the billionaire Shinawatra family, has the support of seven other parties but it is unclear whether it can win over the upper house Senate, which was appointed by an army that forced the party’s last government from office.

Under a constitution written by the military and designed to preserve its political power, members of both houses vote to decide who forms a government, which requires the support of more than half of all MPs.

Move Forward’s anti-establishment agenda and its threat to conservative, old money interests, ensured its bid failed.

Despite Pheu Thai abandoning Move Forward, it said it still hoped to win the backing of its 150 MPs in a prime ministerial vote expected later this month.

“We will hold discussions with Move Forward,” Pheu Thai deputy leader Phumtham Wechayachai said.