Thailand's Constitutional Court declares February's national election null and void.

The poll's been ruled invalid because voting didn't take place in 28 southern districts where candidates were blocked from registering by anti-government protesters.

It's unclear when a new election might take place.

If a new one is organised the protesters say they'll disrupt it again.

The latest twist comes just days after the government lifted a state of emergency in Bangkok to curb political protests.

The demonstrators have been trying since November last year to oust Prime Minister Yingluck Shinawatra.

For now she heads a caretaker administration with limited powers.

She's facing a string of legal challenges which could bring her down including charges related to a rice subsidy scheme that owes money to thousands of farmers.