Lebanon has designated a new prime minister, whose candidacy was proposed by the Iranian-backed Hezbollah movement, a move that risks provoking further political unrest and alienating the country’s Western allies just when Lebanon most needs international support for its rapidly collapsing economy.

Hassan Diab, a little-known engineering professor and former education minister who is from Lebanon’s Sunni Muslim community, was tasked Thursday with forming a government by the country’s Christian party president, Michel Aoun, after a day of consultations with political blocs showed that Diab commanded majority support in parliament.

Few, however, expected his unexpected and controversial selection to survive either the immediate popular backlash that erupted on the streets or the scrutiny of the international community. His appointment not only runs counter to Lebanon’s long tradition of consensual politics but also appears to affirm that Hezbollah is indeed the most powerful political player in Lebanon, potentially deterring future Western aid.

Lebanese leaders have been under pressure for weeks to choose a new prime minister to replace Saad Hariri, who resigned after nationwide protests erupted in Lebanon in October.

Diab’s selection is likely only to deepen the crisis because he doesn’t have the support of Hariri’s majority Sunni bloc, making it harder for him to form a government.

Having been chosen by Hezbollah, Diab will effectively be seen as a candidate of Hezbollah, analysts say.

At a news conference following his designation, Diab said he was independent of any political party. He promised to form a government of “experts” that will implement reforms and fulfill a key demand of the protest movement for a government that does not include the current political parties.

He said his government will be one that “lives up to the expectations of the Lebanese . . . that addresses their concerns, meets their aspirations, reassures them about their future and takes the country from imbalance to stability.”

But within minutes of the announcement, protesters in downtown Beirut began chanting for Diab’s removal. Sunni demonstrators around the country poured onto the streets to burn tires and block roads. “Diab, get out” protesters chanted. “All of them means all of them.”

Under Lebanon’s post-colonial power-sharing agreement, the prime minister is always chosen by the Sunni community, and it is unprecedented for a non-Sunni bloc, such as the Shiite Hezbollah, to anoint a prime minister who does not have majority support among Sunnis, said Maha Yahya, director of the Carnegie Middle East Center.

“The message being sent by Hezbollah to the Sunni community is, ‘We don’t care what you think,’ which is worrisome,” she said.

Political analyst Michael Young tweeted that a government led by Diab “would effectively be a government of confrontation against a majority of the Lebanese people . . . that could quickly turn very ugly.”