''Malaysia does not support the reimposition of the unilateral sanctions by the US against Iran,'' he told the Doha Forum, also attended by Qatari Emir Tamim bin Hamad Al Thani, Reuters reported.
Malaysia and other countries have lost ''a big market'' because of the sanctions on Iran, he said.
''Such sanctions clearly violate the United Nations charter and international law; sanctions can only be applied by the United Nations in accordance with the charter,'' he added.
Back in October, Mahathir said Malaysia was being forced to “make it difficult” for Iranians to live normal lives in the country.
“Our ties are very good with Tehran, but we face some very strong pressures from certain quarters, which you may guess,” he said, without naming where the pressure was coming from.
Banks in Malaysia closed accounts of Iranian individuals and companies, because of US sanctions.
“We are forced to do this because if we don’t, they will close our banks abroad. It’s a kind of bullying by very powerful people.”
The US imposed sanctions over Iran's nuclear program late last year, but Malaysia has maintained good diplomatic ties with Iran.