|PIC1|Iran's supreme leader told visiting Iraqi Prime Minister Nuri al-Maliki on Monday that the presence of U.S. forces in Iraq was the biggest obstacle to its development as a united country.

Ayatollah Ali Khamenei hit out at the "occupiers" in Iraq at a time when Baghdad is negotiating with the United States on a new agreement aimed at giving a legal basis for U.S. troops to stay in Iraq after December 31, when their U.N. mandate expires.

"The presence of occupiers in Iraq, particularly the U.S. armed forces is the main obstacle to unity in Iraq," state radio quoted Khamenei, Shi'ite Iran's top authority, as saying.

"The occupiers who use their military and security powers to interfere in Iraq's affairs are Iraq's main problem," Khamenei said in his meeting with Maliki. He said the "Americans' dreams" in Iraq would not be realised.

U.S. officials have accused Iran of seeking to derail the talks by "inspiring" media reports that the United States is trying to force Iraq to accept a deal on permanent bases.

Ties between Iran and Iraq have improved since the Sunni Arab strongman Saddam Hussein was ousted five years ago, and a Shi'ite-led government came to power in Iraq.

But Maliki's government treads a fine line in its relations with Iran, seeking support while mindful of U.S. accusations that Iran supports the Shi'ite militias responsible for some of Iraq's violence.

Iran, which fought an eight-year war with Iraq in the 1980s, denies the accusation and blames the presence of U.S. troops for the violence that has followed the U.S.-led invasion of Iraq.

Maliki sought on Sunday to soothe Iranian concerns about his government's talks on a "status of forces" deal with the United States, saying: "There is nothing in today's Iraq that could threaten the stability of the neighbouring countries".

The negotiations are the subject of heated debate both in United States and Iraq, where thousands have answered the anti-American cleric Moqtada al-Sadr's call for weekly protests after Friday Muslim prayers.

Iraq's government spokesman said before Maliki's three-day visit started on Saturday that the issue of Iranian interference would be raised, but it was not clear whether it had been discussed in his meetings so far in Tehran.

Iran has often pledged support for Iraq and its government, and Khamenei did so again on Monday: "Helping Iraq is our religious duty," he told Maliki.

To counter Iran's growing influence in Iraq, Washington has been trying to persuade Iraq's Sunni-ruled Gulf Arab neighbours to offer more support to Maliki's government, by forgiving debts and opening diplomatic missions in Baghdad.