Pope Francis, beginning the first trip by a pontiff to Iraq, has made an impassioned call for an end to the militant violence and religious strife that has plagued the country for decades, saying peacemakers should finally be given a chance.

"May the clash of arms be silenced ... may there be an end to acts of violence and extremism," he said, addressing Iraqi President Barham Salih, politicians and diplomats at the presidential palace.

Francis arrived at Baghdad airport under tight security, after telling reporters on his plane that he felt duty-bound to make the "emblematic" trip because the country "has been martyred for so many years".

Hundreds of people gathered in small clusters to see him being driven into Baghdad in a bulletproof BMW, a departure for a pope who normally insists on using small, normal cars.

A motorcade of dozens of vehicles accompanied him out of the airport compound, which recently came under rocket fire from militia groups.

Most of the people along the roads and even some in the presidential palace did not wear masks, despite the risk of coronavirus.

As Francis and the president walked together, the 84-year-old pope limped noticeably, indicating that his sciatica may have flared up again. The condition forced him to cancel several events earlier this year.

In his speech at the palace, Francis criticised factional and foreign interests that have destabilised Iraq and the wider region and hit ordinary people the hardest.

"Iraq has suffered the disastrous effects of wars, the scourge of terrorism and sectarian conflicts often grounded in a fundamentalism incapable of accepting the peaceful coexistence of different ethnic and religious groups," Francis said.

Pope Francis and Iraq's Prime Minister Mustafa al-Kadhem at Baghdad airport

He later paid tribute to people killed in attacks motivated by religion, visiting a Baghdad church where Islamist gunmen killed about 50 worshippers in 2010. Their deaths were a reminder that "violence or the shedding of blood are incompatible with authentic religious teachings", he said.

Iraq's security has improved since the defeat of Islamic State in 2017, but the country continues to be a theatre for global and regional score-settling, especially a bitter US-Iran rivalry that has played out on Iraqi soil.

The US invasion of 2003, after years of international sanctions and a devastating war with Iran instigated by former leader Saddam Hussein in the 1980s, plunged Iraq into sectarian conflict and chronic mismanagement that has plagued it since.

 Iraqi President Barham Salih and Pope Francis during a meeting in Baghdad

The country has deployed thousands of additional security personnel to protect the pope during the visit, which comes after a spate of rocket and suicide bomb attacks.

Francis told reporters on the plane he was "happy to be making trips again" after 16 months of being unable to make foreign trips because of the coronavirus.

The pope's whirlwind tour will take him by plane, helicopter and cars to four cities, including areas that most foreign dignitaries are unable to reach, let alone in such a short space of time.

He will say Mass at a Baghdad church, and travel north to Mosul, where the army had to empty the streets for security reasons last year for a visit by Iraq's prime minister.

Mosul is a former stronghold of Islamic State, and churches and other buildings there still bear the scars of conflict.

Since the defeat of the Islamic State militants in 2017, Iraq has seen a greater degree of security, though violence persists, often in the form of rocket attacks by Iran-aligned militias on US targets, and US military action in response.

The pontiff will also visit Ur, birthplace of the prophet Abraham, who is revered by Christians, Muslims and Jews.