A Thai court has refused to rule on the legality of the country's recent parliamentary election, dealing a blow to the opposition Democrat Party which said the vote was illegal.
The Constitutional Court on Wednesday also rejected a motion by the ruling Pheu Thai party claiming weeks of opposition protests represented an attempt to overthrow the state.
The rulings failed to break Thailand's political deadlock, which has gripped the country since late last year, leaving it with a crippled, caretaker government.
On Tuesday, the election commission said it will hold another round of polls in late April for areas where voting was unable to proceed. A specific date was not announced.
Until enough seats in the lower house of parliament are filled, a new government cannot be formed and Ms. Yingluck's caretaker government will have only limited control over policy.
The Pheu Thai Party is virtually assured to have won the vote, thanks in part to the boycott. Opposition protesters say Yingluck is a puppet of Thaksin, the exiled ex-prime minister who was accused of corruption and overthrown in a military coup in 2006.
The opposition, meanwhile, has refused to end its rallies, despite the imposition of an emergency decree and warnings from government officials. Authorities say arrest warrants have been issued for 19 leaders of the anti-government protests.
The protest movement is supported by many in the urban middle class who are angered by what they say is waste and corruption. At least 10 people have been killed and scores hospitalized during the political upheaval.