The city draws more than 1.5 million Shiite pilgrims each year.

The vast majority hail from neighboring Iran, whose population is overwhelmingly Shiite.

"More than 85 percent are Iranians," said Saeb Abu Ghoneim, president of the hoteliers' union in the city.

Signs throughout the city, 150 kilometers south of Baghdad, are translated into Farsi.

But just days after Washington this month re-imposed sanctions on Iran, following President Donald Trump's decision to pull the US out of a landmark 2015 nuclear accord with Tehran, the impact is already being felt in Najaf, AFP said.

The first round of sanctions against Iran covers financial transactions and imports of raw materials.

Further measures due to hit in November will affect Iran's central bank and the vital hydrocarbon industry.

Cancellations by Iranian pilgrims could have dramatic consequences for Iraq's tourism sector, which last year directly or indirectly employed some 544,500 people, AFP said.

It also contributed three percent of GDP, nearly $5 billion dollars, according to the World Travel and Tourism Council.

Tourism is almost exclusively religious in Iraq and is concentrated in Najaf and nearly Karbala, the country's other holy Shiite city.

As Najaf prepares to welcome pilgrims for numerous religious festivals this month, there is a notable lack of Iranian arrivals.

Transport links have been slashed -- Najaf airport, which used to offer 35 flights a day between the two countries, now operates just 12. 

Officials say most of the passengers on the flights leaving Najaf for Iran are Iraqi pilgrims heading for Iranian holy sites.

To counter the trend, hoteliers have been forced to offer rooms at bargain basement prices.

"Prices have been slashed, to less than 50 percent sometimes," said Youssef Abu Al-Tabouk, owner of Najaf's Al Balad Al Amine hotel.

But discounted stays and other special offers are not enough to make up for the impact of sanctions, the 85-year-old said.

Without Iranian pilgrims, he said, "the market is in free fall".