Iran has strongly criticised US policy in Iraq, blaming the American presence there for sectarian violence.
Mr Mottaki says the US must accept responsibility for the crisis in Iraq
Foreign Minister Manouchehr Mottaki was speaking in Egypt on the second day of a summit of world and regional powers, called to discuss Iraq's security.
The summit, now over, had been expected to see the first high-level US-Iran talks in almost three decades.
Those hopes were dashed, although ambassadors from the US and Iran did hold a face-to-face meeting.
Iraqi Foreign Minister Hoshyar Zebari described the meeting - the second lower-level meeting in three months - as "a positive sign".
But BBC diplomatic correspondent Jonathan Marcus says the meeting will be remembered more for what did not happen, rather than for what did.
Concern for the situation in Iraq but little real action seems to be a fair initial verdict, he says, adding that national reconciliation is, above all else, a job for the Iraqis themselves.
Egyptian organisers did make an effort to bring US Secretary of State Condoleezza Rice and Mr Mottaki together, seating them opposite each other at a formal dinner on Thursday night.
Unfortunately for the Egyptians Mr Mottaki stayed away from the dinner. US officials said he excused himself over the apparently "un-Islamic" dress worn by a violinist entertaining diners.
He was quoted by the Associated Press as saying that a problem with "Islamic standards" was his only reason for not attending.
Iraq's neighbours, including Iran and Syria, had joined ministers from the G8 nations and the EU at the conference in Sharm el-Sheikh.
Mr Mottaki said the US should issue a clear troop-withdrawal plan to return stability to Iraq.
"The continuation of, and increase in, terrorist acts in Iraq originates from the flawed approaches adopted by the foreign troops," he said.
IRAQ CONFERENCE KEY POINTS
Attended by Iraq's neighbours, permanent members of Security Council, EU and G8
International compact signed, aimed at achieving political and economic stability in five years
Iraq won pledges of US $30bn debt relief
US secretary of state talks with Syrian foreign minister
US and Iranian officials met at ambassador level
"The United States must accept the responsibilities arising from the occupation of Iraq, and should not finger point or put the blame on others."
Mr Mottaki also called for the immediate release of five Iranians detained in northern Iraq by US troops in January.
Iraqi Prime Minister Nouri Maliki called for neighbouring countries to stop funding terrorists and to block their entry into the country.
"We will not allow terrorist organisations to use Iraqi territory as a safe haven," Mr Maliki said.
The US has previously accused Iran and Syria of allowing foreign fighters to enter Iraq and of fomenting unrest in the country.
More than $30bn (£15bn) in aid and debt relief was pledged by donors on the first day of the summit.
A five-year agreement was signed offering financial aid but insisting that Iraq pushes towards political reform and reconciliation.
Egypt agreed to write off about $800m owed to it by Iraq while Slovenia, Bulgaria and Poland would cancel 80% of Iraq's debts, the Iraqi finance minister said.
The UK and European Union each pledged $200m in grants.
Meanwhile, US forces in Iraq say they have detained 16 people suspected of smuggling armour-piercing bombs into the country from Iran.
The US army said the smugglers were arrested during military raids in the Sadr City area of Baghdad.