Muslims pray at the Imam Khomeini grand mosque during Eid al-Adha. Picture: Ahmad Halabisaz/Xinhua

Berlin (dap) - Performing an early morning prayer is a ritual of the first day of Eid al-Adha, when Muslims around the world celebrate Islam's holiest festival for four days.

For most Muslims, it is a joyful social gathering that takes place in public squares and arenas.

But Islamophobia, terrorist threats and natural disasters cast a pall over some festivities on Friday, the first day of Eid.

In Italy, several thousand people joined public prayers at a park in Turin and in a square near the train station in Naples, the ANSA news agency said.

"We have to open our hearts to the society in which we live in, show sincerely our hearts and our actions as real Muslims," the imam who led the Turin prayers, Hamid Zariate, was quoted as saying.

But anti-Islam sentiment has risen in Sesto San Giovanni, a suburb of Milan.

It was there, last December, that the terrorist who rammed a vehicle into a Berlin Christmas market was shot and killed by police after fleeing Germany. In the wake of incident, Muslims were denied the use of a sports hall for Eid al-Adha.

The refusal of their request was put down to alleged bureaucratic problems.

"We have celebrated [it] for 20 years in Sesto San Giovanni, in a happy and joyful atmosphere, without any problem. This year, however, the more than 5,000 Muslims of Sesto will be denied the joy of this occasion," local Muslim leader Boubakeur Gueddouda said on Facebook.

In Nigeria, Muslims held Eid prayers under extreme security measures due to the frequency of terrorist attacks on Muslim holidays in the region, with suicide bombers often targeting mosques and prayer grounds.

Nigerian Muslims in Maiduguri had to travel on foot to their celebrations on Friday, after police banned the movement of all motor vehicles, bicycles and even animals in the city of roughly 2.5 million people.

Maiduguri, the capital of north-eastern Borno State, lies at the heart of an insurgency by Islamist terrorist group Boko Haram, which killed an estimated 20,000 people since 2009.

Slaughtering a sacrificial animal is a common Eid ceremony, banned recently in Austria.

Austria's rural Styria province informed sheep and goat farmers that they should not sell to anyone who might kill animals according to Muslim tradition - without legally required stunning or without veterinary oversight.

The official warning against illegal slaughtering ahead of the festivities has caused a stir among Muslim immigrants and progressive-minded farmers.

The letter left farmers wondering how they should detect Muslim customers, while Egyptian expatriates criticized the official warning as discriminatory. A veterinary official has since said that the wording was unfortunate, but he pointed out that 12 men were recently fined for illegally slaughtering 79 sheep during last year's Eid.

Bangladesh was planning on holding scaled-back celebrations this year, since extreme flooding in the north left tens of thousands of people struggling to rebuild homes and crops.

"We can't think of buying a sacrificial animal this year since the flood caused massive loss to my family," said Raihan Azim, a farmer in northern Nilphamari district, which was inundated by floodwaters for more than two weeks.

Bangladesh, where about 90 percent of its 163 million people are Muslim, will celebrate Eid on Saturday. Despite the disaster stretching across a wide swath of the country, tens of thousands have already made their way from major cities to village homes to celebrate the festival with their dear ones.