A coalition of opposition parties in the Central African Republic (CAR) has withdrawn from parliamentary elections after describing the process as a sham.

This comes a day after the constitutional court rejected attempts to annul the first round of voting over allegations of fraud.

The situation in the CAR is extremely precarious as rebels opposed to the re-election of President Faustin-Archange Touadéra have been advancing on the capital, Bangui.

The government accuses the former president François Bozizé of backing the rebels. He denies the accusation.

He was barred from standing for re-election after being accused of murder, torture and other crimes.

The UN says more than 2,000 people have fled their homes in recent weeks.