BAGHDAD - Iranian forces entered southern Iraq before dawn yesterday to seize control of an oil well in disputed territory on the border, a provocation that sent Iraqi security chiefs into emergency meetings, Iraqi officials said.

Senior officials in Baghdad and in southern Iraq said that an unknown number of Iranian troops crossed into Iraq, where they raised the Iranian flag at an oil well in Iraq's part of the Fakkah oil field, one of several fields that Iraq and Iran share. There were no reports of violence or shots fired.

Amir Arshadi, a spokesman for the Iranian Embassy in Baghdad, denied that such an incident took place and criticized the news media for "spreading rumors."

Iraqi Prime Minister Nouri al-Maliki, who spent years in exile in Iran and maintains good relations with leaders in Tehran, summoned his security chiefs for an emergency meeting on the matter, Iraqi state television reported.

"The Ministries of Defense and Interior are in high-level talks with the Ministry of Oil in order to have a clear stance announced by the Iraqi government as to what exactly happened," Interior Minister Jawad al-Bolani said.

The extent of the alleged foray is murky. News agencies quoted some Iraqi officials as saying the Iranians rolled up to well No. 4 in armored vehicles, dug trenches and replaced the Iraqi flag with the Iranian tricolor. Other officials described a much smaller operation, saying it was simply another example of the tug-of-war over the fields.

Sarhan Sami Younes, the head of the security committee for the Maysan Provincial Council, said border commanders told him that three Iranian soldiers crossed the border and stayed for a few minutes. "We have no explanation for why they came in, what they did and how or why they left," Younes said.

Reports of the incident aggravated tensions between the countries, which fought a 1980-88 war that claimed as many as a million lives. Although Iraq's Shiite Muslim-led government and Shiite Iran have grown closer since the 2003 U.S.-led invasion ousted Iraq's Sunni Muslim dictator, Saddam Hussein, border issues remain thorny, with sporadic posturing from both sides.

Border security is one of the main concerns as the American military prepares to withdraw and hand responsibility to Iraqi forces, which remain ill-equipped to prevent the flow of militants and contraband from neighboring countries.

Analysts said that it was too early to say whether the incident would mushroom into greater tensions between the two countries but that it could raise concerns with oil companies looking to invest in Iraq. Oil prices rose slightly after news of the incident.

"It looks like some kind of warning shot, and it could definitely escalate into a big worry for oil companies," said Samuel Ciszuk of the London-based IHS Global Insight.

Iraq has an estimated 115 billion barrels of proven oil reserves, the world's third-largest, behind Saudi Arabia and Iran. Fakkah is the second-largest of the 13 fields Iraq shares with Iran, with reserves of more than 550 million barrels, Iraqis say. Oil analysts put Fakkah's reserves much higher.