BEIRUT — Lebanon is bracing for deepening unrest after weekend riots in the capital suggested the country's once-peaceful protest movement is entering a dangerous new phase.

Rescue services and police said Sunday that more than 400 people were treated for injuries after the worst night of violence since Lebanese took to the streets in October to demand a new government capable of leading the country out of an acute economic and financial crisis.

Protesters and security forces clashed again on the streets Sunday night, with police firing rubber bullets, tear gas and water cannon to disperse demonstrators hurling paving stones, fireworks and other projectiles.

The dark new mood was palpable. “Not peaceful, not peaceful. This is a revolution, not a song,” the protesters chanted in downtown Beirut — pointedly contradicting the “peaceful, peaceful” slogan of the uprising’s early days, when huge demonstrations against the government turned into dance parties.

Heavily armed troops joined riot police at the scene, some carrying shoulder-launched rockets.

“Lebanon is being pushed to the brink of chaos and anarchy,” said Maha Yahya, director of the Carnegie Middle East Center. “This is a country that is spiraling economically downwards, you have increasing frustrations among a young population, and things could get out of hand very quickly. It’s only a matter of time.”

The unrest risks embroiling Lebanon in the accelerating competition for regional influence between the United States and Iran, both of which count allies among rival groups in the tangled political system that the protesters want to reform.

Human Rights Watch condemned what it called the use of “excessive force” by police to disperse protesters. Tear gas filled the streets of Beirut with choking smoke. Videos on social media seemed to show police firing rubber bullets at protesters.

It was clear the demonstrators had sought an escalation. Young men warned onlookers that they planned to attack the security forces. They assaulted police lines with firecrackers, rocks, uprooted trees and potted plants.

The protesters said they had decided on a more forceful approach because three months of peaceful demonstrations had failed to bring about a new government or any easing of the country’s financial and economic crisis. The value of the Lebanese currency has plunged by half in three months, and ordinary people are prevented from accessing their savings as the central bank seeks to stave off financial collapse.

Employers have stopped paying salaries, hospitals are running out of vital medicines, and people are going hungry as the economy skids to a halt.

“People have reached a point of no return,” said Bachar el-Halabi, a lecturer at the American University of Beirut who supports the demonstrators. “They’ve been protesting peacefully on the streets for 90 days, and no one listened to them.”

Some protesters expressed concerns that infiltrators are working to radicalize the demonstrations and push them toward violence to justify harsh crackdowns and deter ordinary citizens from participating. The shift toward more confrontational tactics was accompanied by a noticeable fall in the numbers showing up to the demonstrations.

“There are instigators here,” said Elias, 22, a protester who declined to give his full name as he joined demonstrators at a police barricade blocking access to the parliament ahead of the violence on Saturday. “It’s people who are not with the protests and want to give us a bad name.”

There were instances of violence at protests last year after supporters of the Shiite Hezbollah and Amal movements turned out on the streets to challenge the demonstrators.

The Iran-allied Hezbollah has now signaled its willingness to support the protest movement, even as it pushes for a new government formed exclusively of its allies. The powerful Shiite movement has sent representatives to discuss with the protesters ways it can contribute to their cause, according to representatives of the protesters and politicians allied with Hezbollah.

Hezbollah is exerting pressure for the swift confirmation of a new cabinet led by its nominee, Hassan Diab, a professor at the American University of Beirut who once served as education minister.

Hezbollah hopes that Diab’s appointment will succeed in meeting the protesters’ demands for a government that excludes the traditional political elites widely blamed for the country’s slide into insolvency, according to people involved in the negotiations.

But as the mostly unfamiliar names of the proposed new ministers have leaked to the press, Lebanese have discovered that they have powerful establishment figures behind them. It seems unlikely that the expected announcement of Diab’s cabinet will satisfy the protesters’ demands or the international community’s conditions for offering badly needed economic and financial aid, analysts say.