US President George W Bush has accused Iran and Syria of continuing to support terrorism and warned that the US may take action.
Iran and Syria have been the subject of increasing US attacks
In one of his strongest threats to the two countries recently, Mr Bush said their behaviour was "completely unacceptable" and that any state which continued to support terror "will be held accountable".
He also said their actions hampered peace efforts in the Middle East, calling terrorism "the greatest obstacle to the creation of a Palestinian state".
"Supporting and harbouring terrorists undermines prospects for peace in the Middle East and betrays the true interests of a Palestinian state," he said, during a two-day visit to his Texas ranch by Italian Prime Minister Silvio Berlusconi.
Iran and Syria have been the subjects of increasing attacks by the Bush administration, which considers them state sponsors of terrorism.
Iran was named by Mr Bush as part of an "axis of evil" which also included Iraq and North Korea.
Syria was later added to the list by US officials, as were Libya and Cuba.
Bush's comments come ahead of talks on the Middle East
US anger towards Syria has increased in recent months, and it recently accused Syria of harbouring former members of ousted Iraqi President Saddam Hussein's regime during the Iraqi conflict.
Iran, in turn, has been accused by the US of attempting to develop nuclear weapons.
Iran has vehemently denied the charges and accused the US of encouraging unrest within its borders, following protests by Iranian reformers last month.
Mr Bush also encouraged support of the Palestinian Prime Minister Mahmoud Abbas, also known as Abu Mazen.
"Leaders who are interested in a peaceful solution in the Middle
East must support the efforts of Prime Minister Abbas to build a
democratic Palestine and ease the hardships faced by the Palestinian
people," he said.
The BBC's Rob Watson in Washington says the timing of Mr Bush's remarks appears to be linked to meetings the US president is to hold in the next week or so with Israeli Prime Minister Ariel Sharon and the Palestinian prime minister.
Such strong words, our correspondent says, may be the president's way of demonstrating his commitment to the peace process.
But they may also serve as a warning to all those in the region - including the Israelis and Palestinians - that he expects results, our correspondent adds.