The four members of the influential SOS Chretiens d'Orient (Christians of the Middle East) charity went missing near the French embassy in the Iraqi capital, the organisation's director Benjamin Blanchard told a news conference in Paris.

No ransom demand has been received as yet and no group has claimed responsibility for their disappearance, he added.

SOS Chretiens d'Orient has been working with persecuted Christians in Iraq since 2014 when Islamic State jihadists overran the province of Mosul, displacing tens of thousands of minority Christians and Yazidis.

It is principally active in the Iraqi Kurdish capital Arbil, where many Christians sought refuge.

The missing workers were in Baghdad "to renew their visas and register the association with Iraqi authorities," Blanchard said.

They were also due to inspect the group's activities in the city, including the opening of a new school.

They left their hotel by car for a meeting "which posed no problem," Blanchard said, adding that French and Iraqi authorities were working together to try locate them.

The NGO's director described the men as "experienced staff members who have been working with us for years" and who had "perfect knowledge of conflict zones".

He refused to give the mens' identities.

- Helping Christians remain in Mideast -

The French foreign ministry and the French embassy in Iraq refused to comment on their disappearance.

Baghdad has been gripped by demonstrations for several months.

The protests initially targeted a government widely seen as corrupt and meddling by neighbouring Iran.

But in recent weeks America's military presence in Iraq has become a hot-button issue in Iraq since a US drone strike killed Iranian general Qasem Soleimani and a top Iraqi commander in Baghdad on January 3.

SOS Chretiens d'Orient, which is also active in Syria, Lebanon and Egypt, is one of several Western charities working with Christians in the Middle East.

The aim of the group is to "help Christian communities remain (in the region) and rebuild" their lives, Blanchard said.

The organisation, which is fiercely critical of Islam, portraying it as a threat to Christianity in the Middle East, drew criticism in the past for sending young French volunteers to Syria and Iraq for months at a time.

Photos regularly published by the NGO on Twitter show volunteers visiting Christian families in Arbil and conducting French language classes.

Before the US-led invasion of Iraq in 2003, Iraq's Christian population ran to an estimated 1.5 million.

By the summer of 2019, their number had fallen to around 250,000, Arbil Archbishop Bashar Warda said during a speech in Britain last year.