A Twitter account Iran experts believe is run by the office of Supreme Leader Ayatollah Ali Khamenei said on Tuesday "arrogant" powers had tried hard to bring the Islamic Republic to its knees but had failed.
In a comment apparently referring to the failure of Iran and six world powers to end a dispute about Iran's nuclear goals, a message on the English-language account said: "In the nuclear issue, arrogants have made their best to bring Iran to its knees but they were not able and will not be able to do so."
The term arrogants, or arrogant powers, is used in Iran to refer to the United States and its Western and Israeli allies. Washington cut ties with Tehran a year after the 1979 revolution that ushered in Iran's Shi'ite Muslim theocracy.
Iran and the six powers failed on Monday for a second time this year to resolve their 12-year confrontation over Tehran's nuclear ambitions, and gave themselves seven more months to overcome the deadlock.
In a second tweet, Khamenei appeared to accuse the West of meddling in Middle Eastern turmoil, saying Islamic militants had turned Arab Spring uprisings into Muslim infighting "in line with arrogants' goals".
The message referred to "takfiri" militants - Sunnis who proclaim followers of other sects of Islam to be infidels and therefore legitimate targets of holy war.
A third tweet from the same account said: "US-led coalition against ISIS is a blatant lie. By the means of ISIS, US wants to keep the war among Muslims alive," using an acronym for the Islamic State militant group.
The United States and its allies have launched air strikes on the Sunni Muslim fighters who have seized territory in Syria and neighbouring Iraq.