Pirates hijacked an Italian cargo ship with 18 crew on board at dawn on Tuesday off the coast of Oman in an area notorious for attacks by Somali pirates, officials said.

The Enrico Ievoli, carrying a cargo of caustic soda from the United Arab Emirates to the Mediterranean, was boarded by pirates at around 0400 GMT, said the Naples-based owner of the ship, Marnavi.

"There were 18 people on board," including six Italians, five Ukrainians and seven Indians, Domenico Ievoli, the director of Marnavi, told AFP.

"As far as we know, the Ievoli is currently in movement towards an unknown destination. We presume it's Somalia."

Ievoli said the ship's Italian captain, Agostino Musumeci, had told him: "The pirates are on board but we are all fine."

A foreign ministry spokesman said the Italian Navy, which thwarted a pirate attack against the same ship in 2006 near Yemen, had been alerted.

"Together with the crisis unit, I am closely following the hijacking of the Ievoli," Foreign Minister Giulio Terzi said in a message on Twitter, calling for "strict discretion to ensure a positive outcome".

But the captain's wife, Rita Musumeci, said she had been told of the hijacking by journalists and had had no official word from the government.

"It's shameful. No-one from the state has called us. They're warm with their families. What do they care?" she was quoted as saying by ANSA news agency.

"It's absurd that journalists gave me the news... In these kinds of cases even a small word of comfort can be helpful," she said.

The ministry responded that it was in "close contact" with the families.

Gennaro Ievoli, another Marnavi executive, said the 138-metre (453-foot) ship's cargo, 15,750 tons of caustic soda, was of little value and difficult to steal, adding that "the purpose is probably extortion".

"We will manage to bring them home, all of them, and without a scratch," he said.

Three other hijacked Italian vessels were freed from Somali pirates in November and December, two of them reportedly following ransom payments.

The Savina Caylyn, an oil tanker with five Italians and 17 Indians on board, was freed on December 21 after more than 10 months in captivity.

The foreign ministry denied that the government had paid any ransom and said the liberation was the result of "constant pressure" on Somali authorities.

In November, the Rosalia D'Amato cargo ship with a crew of 21 was also released after seven months in the hands of Somali pirates.

Also in November, British and US commandos freed another Italian vessel, the Montecristo, with seven Italians, 10 Ukrainians and six Indians on board.

According to the International Maritime Bureau, there were 352 reported hijackings worldwide between January and September -- more than half of them carried out by Somali pirates, who often operate far from Somalia's shores.

The European Union Naval Force (EU NAVFOR) anti-piracy mission said earlier this month that Somali pirates were holding 199 people hostage as part of their ransom business.

Since the start of the NAVFOR mission in December 2008, 2,317 seamen have been held hostage for an average of nearly five months.

"This humanitarian tragedy is especially pertinent over Christmas, a time when families normally gather to celebrate," NAVFOR said earlier.

It said many hostages were tortured and abused and some killed by hijackers.

According to Ecoterra International, an environmental and human rights NGO that monitors regional maritime activity and also includes smaller vessels in its tally, pirates hold at least 43 ships and more than 400 seamen.

The Italian government in October signed a protocol with shipowners' association Confitarma allowing the presence of military forces or private guards on board merchant vessels, although it is not yet operational.

Other European countries including Britain, France, Greece and Spain have also made legal arrangements to allow armed guards to board certain vessels.