An unusual plan backed by Kurdish officials in Iraq's Kirkuk province to dig a trench aimed at curbing deadly violence has angered Arab leaders, who call it a land grab.

The trench is merely the latest apparent security measure to raise tensions among Kirkuk's Kurds and Arabs, who both lay claim to the northern province.

For now, workers are digging the 53-kilometre (32-mile) trench -- a defensive measure dating to ancient times -- in the desert to the south and west of Kirkuk city, capital of the eponymous oil-rich province.

Kirkuk is the most important part of a swathe of northern territory that Iraqi Kurds want to incorporate into their three-province autonomous region, a move the federal government in Baghdad strongly opposes.

Diplomats and officials say the dispute is one of the main threats to the country's long-term stability, and it ultimately makes the trench a political as well as a security issue.

"The province took a unanimous decision to build the trench around the city of Kirkuk" to prevent "terrorists from bringing car bombs or stolen or unlicensed vehicles" into the city, provincial Governor Najm al-Din Karim, a Kurd, told AFP.

Karim pointed to a trench around Arbil, capital of Iraq's autonomous Kurdistan region, as an example of the security benefits of such a project.

Arbil and the Kurdish region have largely been spared the deadly violence plaguing the rest of Iraq.

But "the biggest role will still be played by the security forces, and the trench alone is not the only way to control security," Karim said.

He argued that the city's northern and eastern sides are protected by hills and highlands, but Kirkuk's southern and western approaches are flat, thus letting militants bypass security checkpoints.

Kirkuk clearly has a security problem -- it is hit by frequent attacks and is one of the more dangerous areas of Iraq.

In one of the worst single attacks of the year, a suicide bomber detonated explosives in a crowded cafe in July, killing 41 people.

And a car bomb exploded near a Kurdish political party office in the city this week, wounding more than 20 people.

But Arab leaders in Kirkuk see the 3.5-billion-dinar ($2.9-million) trench project as something more than an effort to improve security.

They worry that the trench will serve as a barrier between the city and the southern and western parts of Kirkuk province -- its main Arab-majority areas.

The project is aimed at "isolating Kirkuk, to make it ready to be added to the Kurdistan region," said Abdulrahman al-Asi, head of the Political Council for the Arabs of Kirkuk.

"It is a political collar" aimed at "emptying the Arab component from Kirkuk, so that the Kurds dominate it," he said.

"We will stand against it because it is a dangerous project," he added.

Asi said that "if the purpose is to achieve security goals, we must think of all the areas of the province of Kirkuk, not only the city".

And Burhan al-Asi, a member of the Kirkuk provincial council who boycotted the vote on the trench, said that "it does not protect a thing in Kirkuk".

He called on the government to stop the project, because "it is a trench to isolate Kirkuk".

Governor Karim, however, said "the project serves all the people of Kirkuk, who are Arab and Turkmen in addition to Kurds".

The trench is not the first security measure to run afoul of the rival claims to Kirkuk.

Last year's establishment of the Tigris Operations Command, a Kirkuk-based federal military body covering Kirkuk province as well as neighbouring Salaheddin and Diyala, in turn angered Iraqi Kurds.

Nevertheless, Qassem al-Bayati, the head of the Roads and Bridges Department in Kirkuk, said that the trench will be completed within "the next few weeks", and that several dozen guard towers will also be built along it.

With Iraq grappling with its worst violence in five years and political deadlock paralysing the government, it is unlikely that Kirkuk's security problems or its political future will be resolved any time soon.