"Maybe it is the beginning of an understanding that they must come to some terms with the international community," he told reporters in Lisbon after meeting with Portuguese President Anibal Cavaco Silva.

"We have to prevent nuclear weapons from falling into the hands of Iran but must do everything possible to avoid any sort of conflict," he added in comments broadcast on news radio TSF.

In a surprise move, Ahmadinejad on Monday sent a letter to President George W. Bush, the first direct communication from an Iranian leader in 27 years.

US Secretary of State Condoleezza Rice dismissed the letter, saying it offered "nothing new" to earlier pronouncements by Tehran about its controversial nuclear program.

Kissinger, who served under Republican president Richard Nixon during the tumultuous Vietnam War years, was in Portugal to deliver a speech.