Iran's Foreign Ministry spokesman Hamid Reza Asefi says Iran will never allow U-S warplanes to use its airspace to attack Afghanistan.
He also says Iran will not allow Osama bin Laden -- a prime suspect in last week's terror attacks in the United States -- to enter Iran under any circumstances.
Earlier Thursday, British Prime Minister Tony Blair said a conversation he had with Iranian President Mohammad Khatami gave him hope that Iran could become an ally in the international fight against terrorism.
Iranian media say Mr. Khatami urged restraint by Washington to avoid a human catastrophe in Afghanistan.
In recent days, Iran has spoken out strongly against the terrorist attacks on the United States -- while mounting a diplomatic drive to head off possible U-S military strikes in neighboring Afghanistan.
Meanwhile, the central Asian republics of Tajikistan and Uzbekistan are denying a Washington Post report that they had agreed to allow U-S warplanes to use their bases.
Officials of both republics say they have not received any official requests from Washington regarding aircraft basing.