Turkey will keep buying natural gas from neighbouring Iran as Western allies raise pressure over Tehran's disputed nuclear programme, Energy Minister Taner Yildiz said on Wednesday.

"It is out of question for us to take a step backward," Yildiz was quoted as saying by the Anatolia news agency. "Furthermore, we have not been asked to take such a step."

Iran is Turkey's second biggest natural gas supplier after Russia, and Yildiz said that Tehran supplies 18-20 percent of the gas that Turkey consumes.

On November 30, the US Senate unanimously approved new economic sanctions aimed at further crippling Iran's energy, shipping and port sectors a year after the Congress passed tough restrictions against Tehran.

The latest US proposal is expected to sail through the US House of Representatives and be signed into law by President Barack Obama.

Iran's economy is struggling to cope with tightening sanctions imposed by the United States and the European Union over the past two years.

An EU measure which took effect in July halted European purchases of Iranian crude oil, and has since caused Tehran's oil exports to Asian customers to decline by between 10-30 percent.

On December 7 however, the United States extended exemptions from sanctions designed to choke Iran's oil exports to nine major economic powers, including Turkey, China, Taiwan, India and South Korea.

Yildiz noted on Wednesday that the Turkish oil refiner TUPRAS has continued to import crude oil from Iran.

"Unlike some European countries, Turkey is not a country which imports three-five percent of its needs from Iran," the minister explained in a reference to crude oil shipments.

"Last year, Turkey met almost half of its needs from Iran. It is an important source of imports therefore."

Yildiz added that Turkey had bought more oil from Libya, Saudi Arabia and Russia to make up for declining crude imports from Iran due to US-EU sanctions.