More than 200 Iranian lawmakers issued a joint statement on Wednesday criticising what they called Saudi Arabia's "role" in suppressing protests in Bahrain and Yemen, the parliament's website reported.
"The killing of innocent people in these two countries, in light of Saudi Arabia's role, shows the weakness of the governments," in Manama and Sanaa, said the statement signed by 210 MPs of the 290-seat parliament.
The statement called on the United Nations to send a delegation and investigate the human rights situation and to "stop Saudi Arabia's interference in the internal affairs" of the two countries.
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The lawmakers also denounced "the West's silence" in the face of "savage suppression."
Iran has vocally supported most uprisings in the Arab world, with the exception of the revolt in its regional ally Syria, where it backs the regime of President Bashar al-Assad while advocating reforms.
Tensions between Iran and Saudi Arabia rose sharply in March when Saudi troops intervened in Bahrain to help the Gulf kingdom's Sunni ruling family suppress month-long protests led by its Shiite majority community.
The Saudi intervention triggered angry protests from Tehran, also heightening tensions with other Gulf monarchies.
Iran has also slammed the Riyadh-backed crackdown on protesters in Yemen.