NASIRIYAH, Iraq - Iranian forces took control of a southern Iraqi oil well on a disputed section of the border on Friday, US and Iraqi officials told AFP.
"There has been no violence related to this incident and we trust this will be resolved through peaceful diplomacy between the governments of Iraq and Iran," a US military spokesman told AFP at Contingency Operating Base Adder, just outside the southern Iraqi city of Nasiriyah.
"The oil field is in disputed territory in between Iranian and Iraqi border forts," he said, adding that such incidents occur quite frequently.
An official of the state-owned South Oil Co in the southeastern city of Amara, and west of the field, said: "An Iranian force arrived at the field early this morning (Friday).
"It took control of Well 4 and raised the Iranian flag even though the well lies in Iraqi territory," the official added.
"An oil ministry delegation is to travel to the area on Saturday to assess the situation."
The national security council was due to hold an emergency meeting on Friday chaired by Prime Minister Nuri al-Maliki, Iraqi state television said quoting the minister of state for national security, Shirwan al-Waili.
The council also groups the ministers of interior, defence, foreign affairs, justice and finance.
Well 4 lies in the Fauqa Field, part of a cluster of fields Iraq unsuccessfully put up for auction to oil majors in June. The field has estimated reserves of 1.55 million barrels.
The field is about 500 metres (yards) from an Iranian border fort and about 1 kilometre from an Iraqi border fort, US Colonel Peter Newell said, adding that it falls on the Iraqi side of a border agreed between the two countries.
There are five other similar fields that also fall into disputed territory, he said.
"What happens is, periodically, about every three or four months, the oil ministry guys from Iraq will go ... to fix something or do some maintenance. They'll paint it in Iraqi colours and throw an Iraqi flag up.
"They'll hang out there for a while, until they get tired, and as soon as they go away, the Iranians come down the hill and paint it Iranian colours and raise an Iranian flag. It happened about three months ago and it will probably happen again."
He added that the Iraqis are "very concerned about the Iranians pulling oil out of fields underneath Iraq."
Iran has prevented Iraqi oil officials from reaching the well in the past, an industry source said. The Iraqis have accused Iran of firing on their people, something Tehran has denied.
There have been a number of meetings in recent years aimed at reaching agreement on border fields, so far without success.