The Constitutional Court has ruled that Thailand's most recent general election was invalid.

The February 2 vote was unconstitutional because votes in 28 constituencies could not take place on the same day as elsewhere due to opposition protests preventing candidates from registering, the court held.

Court secretary-general Pimol Thampitakpong said: "The process is to have a new general election."

But a spokesman for Prime Minister Yingluck Shinawatra's For Thais Party said it would not respond until it had studied the ruling.

Thais would "play by the rules under democracy and by non-violent means, no matter how much we are bullied," said Prompong Nopparit.

"The reason this election is nullified is because the polls were blocked by protesters. We've played by the rules all along, but what about the other side?"

February's election was called after Ms Shinawatra asked the king to dissolve parliament amid attempts by the opposition Democrat Party and People's Democratic Reform Committee to bring down her elected government and replace it with an unelected "people's council."

But the Democrat Party boycotted the poll and sabotaged voting in many areas, meaning no result could be declared.

Democrat spokesman Chavanond Intarakomalyasut said that the court's ruling was "the beginning toward the solution to the nation's crisis" but only pledged to participate in an election "when it's accepted by all sides."

Electoral Commission president Supachai Somcharoen said it would take at least three months to organise another election, raising tensions in a country where the military seized power in 2006 ahead of a planned rerun.

Protest movement spokesman Akanat Promphan hinted that the opposition would make a bid to tweak the law in its favour before agreeing to a new poll. The neoliberal Democrats haven't won since 1992.