Ex-Georgian president assails Ukraine president at mass Kiev rally

Saakashvili's warning at a demonstration outside parliament in the capital was the culmination of a month of anti-government protests the one-time Poroshenko ally has led across Ukraine since returning to the country last month.

"There can be no fight against corruption while Poroshenko is in power," Saakashvili said.

"It is time for them to hear us," the 49-year-old said to chants of "Shame!" and "Out with the gang!"

The national police department said an anti-riot officer and three demonstrators were hurt in scuffles that involved nearly 5,000 people in the heart of Kiev.

Poroshenko was a Western favourite who rose to power when a bloody 2014 revolution toppled a Kremlin-backed regime and pulled Ukraine out of Russia's historic orbit.

But Poroshenko's critics fear that he has put the breaks on institutional changes and the difficult task of eliminating state graft in order to preserve the existing political order.

The complex relationship between Saakashvili and Poroshenko has had twists and turns that exemplify the difficulties facing crisis-torn Ukraine.

Saakashvili was a fierce Poroshenko supporter who became a regional Ukrainian governor after serving two terms as Georgia's president before fleeing that country under pressure from the new regime.

Yet Saakashvili became more disgruntled with time and eventually accused Poroshenko himself of being the corruption kingpin.

The charge saw Saakashvili lose his Ukrainian citizenship while he was paying a visit to the United States in July.

Saakashvili made a dramatic return to Ukraine with the help of hundreds of supporters in September and the protest in Kiev on Tuesday marked his sternest face-off with Poroshenko to date.

Poroshenko did not address the corruption allegations on Tuesday and just told reporters: "I view the protests with understanding and respect its participants".

Three demands

The protesters issued three major demands for the country's president.

The most crucial involved stripping lawmakers of immunity from prosecution and launching an anti-corruption court that Kiev's lenders at the IMF have labelled a "benchmark" of Ukraine's progress toward Western standards.

A third demand called for changes to the election system that would help independent lawmakers gain seats.

Tuesday's rally was called by several political parties besides Saakashvili's which have also opposed Poroshenko's rule.

These included one led by former premier Yulia Tymoshenko and the Samopomich (Self-Reliance) movement that was first elected to parliament in 2015.

The three are currently united by a deep-seated antipathy toward Poroshenko.

Yet it is unclear how long their union will last since each appears to have its own political ambitions.

Mounting pressure

Poroshenko appeared to respond to the mounting political pressure by introducing a bill on Tuesday that would eliminate lawmakers' immunity starting in 2020.

But protest organisers dismissed this as a token measure that needlessly delayed the long-promised change.

"In order to start political reforms, we have to have a regime change," university lecturer Taras Tretyak told AFP as protesters sang and chanted around him.

"Unfortunately, Ukraine is in such a state that the issue of conducting reforms is one of the country's very survival," the 37-year-old said.

Lawmakers can currently be charged with a crime only if a majority in parliament votes to remove their legal protection.