Thousands of people have taken to the streets in Iraq's capital, Baghdad, after Shia leader Muqtada al-Sadr called for a "million-strong" march to demand the withdrawal of US troops from the country, putting the protest-hit city on edge.

The demonstration on Friday added an extra layer to the months-old protest movement that has gripped the capital and the Shia-majority south since October, demanding a government overhaul, early elections and more accountability.

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In the early hours of Friday, protesters, including men, women and children of all ages, carried Iraqi flags and marched under grey skies.

Loudspeakers blasted "No, no America!" at a central square in Baghdad. A child held up a poster reading, "Death to America. Death to Israel."

The US military presence in Iraq has become a hot-button issue in the country since a US drone attack killed Iranian general Qassem Soleimani and Iraqi militia commander Abu Mahdi al-Muhandis on January 3 outside Baghdad's international airport.

Two days later, parliament voted for all foreign troops - including some 5,200 US forces - to leave the country and called on the government to cancel its request for assistance from the US-led coalition that had been working with Baghdad to fight the ISIL (ISIS) group.

The vote was non-binding, however, and a senior US official said on Thursday that Washington had yet to open talks with Baghdad on a troop pullout.

Al-Sadr, whose party won the most number of seats in the May 2018 parliament elections, seized on the public anger over the drone attack to call "a million-strong, peaceful, unified demonstration to condemn the American presence and its violations".

Iraq's top Shia Muslim leader, Grand Ayatollah Ali al-Sistani, later called in his weekly sermon for political groups to form a new government as soon as possible to bring stability to the country and enact reforms to improve Iraqis' lives.

He also reiterated his opposition to foreign interference in Iraq, having previously condemned the US killing of Soleimani.

"Iraq's sovereignty must be respected ... and citizens should have the right to peaceful protest," he said.

'We don't want America here'

Friday's rally is supported by mainstream Shia parties, including al-Sadr's political rival Hadi al-Ameri, who heads the Fatah bloc in parliament, as well as the Popular Mobilisation Forces (PMF, or Hashd al-Shaabi), an umbrella group comprised of an array of militias, including Iran-backed groups.

Al Jazeera's Imran Khan, reporting from the protest, said the turnout was a "real show of strength".

"It almost doesn't matter if this is a million people or less. The size and the vocalness of the crowd has made sure that the message has been sent now."

There was a heavy security presence as the protesters, mostly hailing from the capital but also Iraq's southern provinces, walked on foot to an assembly point in Baghdad's Jadriya neighbourhood, waving Iraqi flags and wearing symbolic white shrouds.

Mariam, second from right, and her family [Linah Alsaafin/Al Jazeera]

"I came today to protest against the US being in our lands," Mariam, 18, told Al Jazeera.

"We want to liberate our country from these chains of oppression. We have been suppressed and hurt by the US's own interests in the region so we want them out of Iraq."

Aliya al-Ajeel, a mother from Sadr City, said: "The US occupation has taken everything from us. We have nothing left."

"Since 2003, we have been stripped from our basic dignity and right to live a normal life. We're living in decrepit houses; we have no jobs, no salaries. We don't want America here."

Linah Alsaafin contributed to this report from Baghdad, Iraq