Tehran: Iran's top leader says the US is using "money and sex" to try to infiltrate the Islamic Republic and warns Iranians not to fall into the "enemy's trap".

In remarks to commanders of the elite Revolutionary Guard today, Ayatollah Ali Khamenei says authorities should take concerns about "infiltration" seriously and that political factions should not use the issue against each other.

His comments appeared to lend support to a recent wave of arrests of pro-Western writers and journalists, which hard-liners in the judiciary and security services have said is necessary to prevent Western infiltration.

Iran's moderate President Hassan Rouhani has criticised the arrests.

Khamenei, who has the final say on all matters of state, has long believed that the United States is bent on overthrowing the Islamic Republic.