Tens of thousands of opposition protesters pack the streets of Cambodia's capital, Phnom Penh.

They are demanding a probe into a July election that returned long-time Prime Minister Hun Sen to power.

The demonstrators say the vote was rigged.

Led by opposition figure Sam Rainsy, they accuse the ruling Cambodian People's Party of tampering with ballot boxes and leaving voters off the electoral roll.

"We're praying for one reason, one purpose, which is praying for peace, freedom and justice," said Rainsy.

Many in the crowd echoed that call.

"I want justice for myself and for the Cambodian people, to find justice for their vote."

The protests are perhaps the biggest challenge Hun Sen has faced during two decades of iron-fisted rule.

While Cambodia's economy is growing quickly, the demonstrations have been fed by widespread anger over rising inequality and land rights

The Cambodian People's Party has denied foul play and Hun Sen says he