Senior Bush administration officials have issued new warnings to Iran not to interfere in the reconstruction of Iraq.
Rumsfeld: Iran being "unhelpful" regarding Iraq
Tehran was also told to do more to tackle terrorism despite its claims that it has arrested members of Osama Bin Laden's al-Qaeda network.
US Defence Secretary Donald Rumsfeld was one of those with strong words for Tehran, warning that any attempt by Iran to build an Islamic republic in its neighbour Iraq would be quashed.
He told the Council of Foreign Relations that Iran was "being unhelpful today with respect to Iraq".
"Iran should be on notice; efforts to try to remake Iraq in Iran's image will be aggressively put down," Mr Rumsfeld said.
In the same speech, Mr Rumsfeld acknowledged that Iraq may have destroyed all its chemical munitions and weapons of mass destruction before the US-led invasion last March.
He said this may explain why such weapons were not used against coalition forces during the recent conflict.
The defence secretary's comments about Iraq came amid further accusations from Washington that Tehran has been harbouring fugitive members of Osama Bin Laden's al-Qaeda network and trying to develop nuclear weapons.
White House spokesman Ari Fleischer said on Tuesday that steps Iran had taken regarding the capture of al-Qaeda suspects were "insufficient", despite the country's arrest of several suspected members on Monday.
He also said the US continued to suspect that weapons development was at the heart of Iran's nuclear industry.
Iran has denied all the allegations, with foreign ministry spokesman Hamid Reza Asefi saying he hoped the US would "avoid taking an interventionist stance".
The heat on Iran is likely to be turned up even further on 16 June if - as Washington hopes - the International Atomic Energy Agency signals grave doubts that Iran's network of nuclear facilities are merely designed for power generation.
The issue of Iran is said to have revived the split between moderates in the Bush administration who favour diplomacy and hardliners who prefer more robust action.
The issue of Iraqi weapons programmes has proved contentious
On Tuesday a meeting between top US officials on Iran was reportedly suspended until Thursday, US officials told Reuters news agency, which observers say may be due to such a split.
Iran suspects hardliners in Washington of moving to undermine or change Iran's Islamic system, the BBC's Jim Muir in Tehran says, while the US in turn is worried that Islamic factions may try to install a theocracy-like government in Baghdad, echoing the Iranian regime that came to power in the 1979 revolution.
Washington also accuses Tehran of links to suicide attacks on Western targets in the Saudi capital Riyadh earlier this month which killed 34 people.