The head of Iraq's Governing Council, Jalal Talabani, has urged Iraq's neighbours to crack down on "terrorists" crossing into Iraq.
The US says foreign terrorists are slipping into Iraq
Mr Talabani said terrorists had entered from Syria, Saudi Arabia and Iran, and he urged them to do more to control their borders with Iraq.
Syria, meanwhile, has urged America to withdraw its troops from Iraq.
A Syrian foreign ministry spokeswoman said the US occupation of Iraq had led to a rise in terrorism there.
Terrorists 'getting through'
The United States has said it believes the people behind recent attacks in Iraq have come in from neighbouring countries.
Last month, President George W Bush warned Syria and Iran to do more to prevent terrorists crossing into Iraq, saying he expected them to "enforce borders".
Mr Talabani said he was not accusing Iraq's neighbours of being behind the infiltrations, but said they had failed to stop them, the Arabic news station al-Jazeera reported.
The head of the Governing Council said he will visit Iran, Syria and Turkey later this month.
He said he wanted to "ease the atmosphere" with Turkey after the Governing Council opposed Ankara's decision last month to deploy Turkish troops in Iraq.
'America the problem'
In an interview with a Saudi newspaper on Wednesday, Syrian foreign ministry spokeswoman Bushra Kanfani called on the United States to withdraw from Iraq.
"The problem is America, not Syria," Ms Kanfani told Asharq al-Awsat.
"America must be more objective, because when it entered Iraq there was no terrorism
and now there is the problem of terrorism and of al-Qaeda - and the matter has changed from one of weapons of mass destruction and toppling a regime to a new one of terrorism," she said.
Ms Kanfani said Syria was "doing what we can" to stop terrorists crossing its border with Iraq, adding that America should make a greater effort to control Iraq's borders.