By Christopher Gunness BBC East Asia Today, Phnom Penh

Speaking to the BBC, Princess Norodom Vacheara accused party leader Prince Norodom Ranariddh of appointing "corrupt ministers".

She said if this happened again after this Sunday's general election, she would leave the party.

More than 20 parties are running in Sunday's election

Princess Vacheara is a powerful member of Funcinpec and this unprecedented public attack on Prince Ranariddh is likely to send shockwaves through the party.

Funcinpec, as the junior partner in the ruling coalition, has 11 ministers in the Cambodian cabinet.

And although Princess Vacheara also criticised the party of Prime Minister Hun Sen as corrupt, her comments are likely to infuriate the prince.

Prince Ranariddh is the junior partner in the ruling coalition and sources close to the prime minister have told the BBC that private discussions are going on with Cambodia's third party, the opposition Sam Rainsy Party, about forming a possible coalition.

Much depends on the outcome of Sunday's vote.

If, as many predict, the Sam Rainsy Party fairs well, then it could force Prince Ranariddh out of government.

This would be a serious blow to party morale and might signal the beginning of the end of direct royal involvement in Cambodian politics.