"The enemies of Islam and Muslims want to create discord among Muslims in the world ... so having unity is the most important need of the Islamic world," he said in a meeting with state officials on the occasion of the Prophet Mohammad's birthday.
Iran is at odds with the West over its nuclear programme which Washington and its allies fear could allow it to acquire atomic weapons, something Tehran says it does not intend to do.
Iran's Sunni Muslim neighbors, many of which, like Saudi Arabia, have strong ties with the United States, are also wary about Iran's nuclear ambitions. Khamenei said the West had a deliberate policy of sowing distrust among Muslim nations.
"Unfortunately, despite agreement on the need of defending occupied Islamic territories, the Islamic world has been influenced by the American and British propaganda and plots to create discord among Shiites and Sunnis," he said. "Bullying powers, America and Britain are fully aware that disunity and discord among Muslim can deviate the Muslims' public opinion from the important issue of Palestine." Opposition to Israel, which sees Iran's nuclear program as a threat to its existence, has been a cornerstone of the Islamic republic since 1979 and Iran backs Palestinian and Lebanese militant groups opposed to peace with the Jewish state.
"The occupation of the holy land of Palestine and the endless brutality of the Zionist regime toward innocent Palestinian people is a big wound in the body of the Islamic world," Khamenei said, calling Israel a "dangerous and fatal cancer.” Parts of the speech were carried on state television.
Israel has not ruled out military action if diplomacy fails to resolve the nuclear row.Iran, the world's fifth-largest crude exporter, has vowed retaliation for any attack.