Beirut (AFP) - Hundreds of thousands of protesters rallied Sunday across Lebanon to condemn official corruption and demand the government resign, on the eve of a deadline for politicians to accept a reform package.

They were the largest rallies yet in a four-day wave of protests that have gripped the Mediterranean country, the biggest such movement in years which brought to a standstill the capital Beirut, second city Tripoli and other major towns.

The demonstrations have crippled the country and threatened the government of beleaguered Prime Minister Saad Hariri, who has given cabinet members until Monday to support his reform plan.

Sunday a cabinet official, speaking on condition of anonymity, told AFP that Lebanon's main parties have agreed to the proposals which Hariri hopes the government will adopt at a session Monday.

"He sent it to all factions and received their agreement, especially from the Free Patriotic Movement and Hezbollah, and tomorrow he will go to the cabinet to approve it," he said, naming two key coalition partners who are opposed to the government's resignation.

Across the country, protesters waved the national flag and chanted "revolution" or "the people demand the fall of the regime", echoing slogans from the 2011 Arab Spring uprisings that toppled governments.

Lebanon's protests have grown steadily since public anger first spilled onto the streets Thursday evening in response to a proposed tax on calls via WhatsApp and other messaging services.

While the government quickly dropped that plan, the leaderless protests morphed into demands for a sweeping overhaul of the political system, with grievances ranging from austerity measures to poor infrastructure.

The cabinet official said the reform plan was not intended to impose further taxes, but would include privatisation in some sectors.

But many Lebanese were unimpressed with the news.

"Cancelling taxes is not enough. We want corruption to be held to account. We want our money back," said Hassan, a tradesman.

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Protestor Rana Medawar agreed.

"They have been lying for more than 20 years. We are fed up and we want all the politicians to go," she said.

- 'Thieves' -

More than a quarter of Lebanon's population lives below the poverty line, the World Bank says, while the political class has remained relatively unchanged since the end of a devastating 15-year civil war in 1990.

Lebanon ranked 138 out of 180 in Transparency International's 2018 corruption index, and residents suffer chronic electricity and water shortages.

The political system was set up to balance power between the country's religious sects, including Christians, Sunni Muslims, Shiite Muslims and Druze.

Critics say it entrenches political patronage and pits citizens against each other along sectarian lines.

On Sunday, protesters called out the names of some politicians, with the crowd responding with swear words.

Zalfa Aboukais, 27, hung signs bearing the names of lawmakers and ministers on barbed wire near parliament and the seat of government, saying they were all "thieves".

She said she was protesting "against the hooligans who have been in power for 30 years".

Mustafa said he had been demonstrating for three days.

"I will continue to protest because I want a future in this country and I want to live in dignity," he said.

President Michel Aoun is due to chair a meeting of the government on Monday morning to discuss Hariri's reform package.

The cabinet official said some of Hariri's traditional allies have expressed reservations over the plan.

On Saturday Samir Geagea, head of the Christian Lebanese Forces militia, said he was pulling out his four ministers from the cabinet.

- Paddling pool, disco -

Lebanon is on the brink of economic collapse and the government had been weighing a raft of new taxes to shore up finances and secure $11 billion in aid pledged by international donors last year.

It is one of the world's most indebted countries, with a deficit of around $86 billion -- more than 150 percent of gross domestic product -- according to the finance ministry.

Public anger surged after parliament passed an austerity budget in July as part of efforts to unlock the $11 billion.

What some have dubbed the "WhatsApp revolution" has support from wide swathes of Lebanon's society and the protests have been mostly good-natured, with people singing or launching into traditional dabke dances.

In Beirut, some demonstrators camped out in a paddling pool, while late at night in Tripoli Lebanese waved their mobile phone lights and danced as the protest morphed into a giant open-air nightclub.

"It's time for a change," said Nazih Siraj a 50-year-old in Tripoli, adding he was demonstrating for the future of his four daughters.

On Sunday, Lebanese expats also gathered to demonstrate in Paris, Los Angeles and Washington.