The head of the United Nation's refugee agency Ruud Lubbers says in the event of a war in Iraq up to 600,000 people could try to flee the country.
Half the total would probably head for Iran while the remainder is expected to make their way to Turkey, Syria and Jordan.
The UN and neighbouring countries are drawing up contingency plans for a possible outflow of refugees from Iraq.
UN estimates
The UNHCR insists that the figures are purely planning figures - it has, it says, no inside knowledge about what might happen in Iraq.
But it clearly believes that two countries could well bear the brunt of any Iraqi refugee movements - Iran, and to a lesser extent, Turkey.
Mr Lubbers said that, broadly speaking, Shi'ites from the south and people from central Iraq could be expected to head for Iran, while those from the Kurdish administered north would set out for Turkey.
Some refugees might also go to Syria or Jordan.
But the UNHCR chief believed it unlikely that many would head for Kuwait because of its heavily fortified border.
Kuwait has announced that it is establishing a military exclusion zone on its northern border with Iraq from 15 February.
Mr Lubbers said Saudi Arabia had a policy of keeping its borders closed but would probably offer support to regional countries such as Jordan if they took in Iraqi refugees.
Preparations
Iran and Turkey have already begun planning for a possible humanitarian crisis, positioning supplies along their borders.
But both would clearly prefer to help any refugees inside Iraq itself, rather than on their own territory.
If war were to break out, it is not entirely clear how Iraq's neighbours might react.
UNHCR spokesman Kris Janowski said the agency had made its standard appeal for neighbouring countries to keep their borders open to refugees.
Asked whether they had promised to do so, he said none of them had said a categorical "No."