Moktada al-Sadr, an influential populist Shi’a leader in Iraq, called Tuesday for renewed protests against Prime Minister Nuri Kamal al-Maliki.

Joining Iraqi Sunnis and Kurds in their opposition to the Prime Minister, Mr. Sadr claimed that Mr. Maliki bears “full responsibility” for current unrest in Iraq, and warned that “the Iraqi spring is coming,” according to an article published in the New York Times. Mr. Maliki is widely suspected of moving to gain control over armed groups in the country to consolidate his power, resonating unpleasantly with memories of Saddam Hussein’s 24-year dictatorship.

Demonstrations against Mr. Maliki began in Sunni areas last month, following the raid of Sunni Finance Minister Rafia al-Issawi’s home by security forces. The raid was seen as an attempt by Mr. Maliki to weaken Sunni rivals within the government, and resulted in immediate and lasting political fallout.

Last week tens of thousands of Sunni Muslims blocked Iraq’s main trade route to neighbors Syria and Jordan. Just yesterday Sunni protestors in the western province of Anbar set up a tent city near Ramadi, the province’s capital, to protest Mr. Maliki’s government.

“We are with the demonstrators, and Parliament must be with them, not against them,” Mr. Sadr said. “The legitimate demands of the demonstrators, by which people know what they want, should be met.”

Ethnic, sectarian, and political tensions among Iraq’s Kurdish, Arab, Sunni and Shi’a populations have generated escalating violence across the country, along with political gridlock. Iraq Body Count, a nonprofit group, tallied at least 4,471 civilian deaths from attacks in 2012, up from 4,136 in 2011.

“Over all, 2012 has been more consistent with an entrenched conflict than with any transformation in the security situation for Iraqis in the first year since the formal withdrawal of U.S. troops,” the nonprofit group said.

Adding to friction with western Sunni groups, tensions between Mr. Maliki’s government in Baghdad and Kurds in the oil-rich north have risen recently as soldiers squared off with Kurdish militias. The Kurdish regional government has now signed 48 oil contracts without Baghdad’s consent, and the infuriated national government seeks a larger share in the region’s oil revenues.

Elected as Iraqi Prime Minister on May 20 2006, Nouri al-Maliki began his political career as a Shi’a dissident under Saddam Hussein’s despotism in the late 1970s. A government-issued death sentence forced Mr. Maliki into exile for 24 years, bringing him national recognition and a leading role in the prominent Islamic Dawa Party upon his return. Moderate Iraqis, both Shi’a and Sunni, now fear he is heading toward dictatorship.

Moqtada Sadr is fanning the flames of public discontent, potentially with an eye on provincial council elections in April 2013. Despite the lack of an official title in the Iraqi government, Mr. Sadr has emerged as a mainstream political leader through vocal and often violent opposition to the American occupation.

In 2003 Mr. Sadr famously told 60 Minutes’ Bob Simon that “Saddam was the little serpent, but America is the big serpent.” Mr. Sadr established the Mehdi Army that same year, a militia group involved in fierce fighting with US forces from 2004 onward.

The Sadrist movement shares numerous characteristics with Lebanon’s Hezbollah, another Shiite movement that has combined faith, social works and a military wing to achieve power.

Having initially exerted his political influence to appoint Mr. Maliki, a fellow Shi’a, as Prime Minister in 2005, Mr. Sadr’s calls for anti-government protests now threaten to topple a fragile regime beset by political, religious, and ethnic divides.

Unless Mr. Maliki makes a concerted effort to accommodate the powerful Sadrist movement and reach beyond his core Shi’a constituency, the country risks a disastrous return to broad sectarian strife and even greater bloodshed in 2013.