A political bloc led by populist cleric Moqtada al-Sadr, a long-time adversary of the United States who also opposes Iranian influence in Iraq, has won the country's parliamentary election, the electoral commission said on Saturday.

Sadr himself cannot become prime minister as he did not run in the election, though his bloc's victory puts him in a position to have a strong say in negotiations. His Sairoon electoral list captured 54 parliamentary seats.

The Victory Alliance, headed by incumbent Prime Minister Haider al-Abadi, trailed in third place with 42 seats, several seats behind the Al-Fatih bloc, which won 47 seats.

Al-Fatih is led by Hadi al-Amiri, who has close ties with Iran and heads an umbrella group of paramilitaries that played a key role in defeating Islamic State.

The results were announced a week after Iraqis voted in a nationwide election, which produced surprising results amid historically low turnout.

Winning the largest number of seats does not automatically guarantee that Sadr will be able to hand-pick a prime minister.

Since no electoral list won an outright majority, negotiations to form a government are expected to drag on for months.

Parties will have to align themselves to try and form a block large enough for the parliamentary majority necessary to nominate a candidate.

"Your vote is an honour for us," Sadr tweeted moments after the official results were announced in the early hours of Saturday morning. "We will not disappoint you."

Rebuke

The victory was a surprising change of fortunes for the Shi'ite cleric. Sadr, who made his name leading two violent uprisings against US occupation troops, had been sidelined for years by Iranian-backed rivals.

His bloc's performance represented a rebuke to a political elite that some voters blame for widespread corruption and dysfunctional governance.

It was also bolstered by a historically low turnout across the country, estimated earlier in the week at 44.5 percent. Sadr maintains a loyal base of supporters who turned up to the polls amid widespread national apathy.

Sadr's unlikely alliance with communists and secular Iraqis says it fiercely opposes any foreign interference in Iraq, which is strongly backed by both Tehran and Washington.

It has promised to help the poor and build schools and hospitals in Iraq, which was battered in the war to defeat Islamic state and has suffered from low oil prices.

Before the election, Iran publicly stated it would not allow Sadr’s bloc to govern.

The election dealt a blow to Abadi, but he could still emerge as a compromise candidate palatable to all sides because he has skillfully managed the competing interests of the United States and Iran - unwitting allies in the war against Islamic State - during his term in office.

Amiri is regarded as one of the most powerful figures in Iraq. He spent two decades fighting Saddam Hussein from Iran.

Iranian Major General Qassem Soleimani, commander of foreign operations for Iran’s elite Revolutionary Guards and a highly influential figure in Iraq, has been holding talks with politicians in Baghdad to promote the formation of a new cabinet which would have Iran’s approval.

Earlier on Saturday, Sadr met a group of ambassadors from neighboring countries, including Turkey, Jordan, Syria, Kuwait and Saudi Arabia.

During the meeting, Sadr called for a strengthening of ties with neighboring states which have "historical and cultural ties with Iraq", according to a statement from his office.

Sadr visited Riyadh late last year, signalling a possible rapprochement with Saudi Arabia which has been tentatively seeking to increase its involvement in Iraq.

The government should be formed within 90 days of the official results.