Turkey's Erdogan challenges accusers to prove it buys energy from Islamic State

Turkey only procures oil and gas from known sources and those who accuse it of buying from Islamic State need to prove their accusations, President Tayyip Erdogan said on Thursday.

Speaking to a group of local officials in the capital Ankara, Erdogan also said that Turkey was taking precautions to stop oil smuggling at its borders, a key source of revenue for the Islamist militant group.

He also renewed his call to parliament to draft a new constitution that will grant his office greater executive powers, arguing it better suits affluent nations.

"Look at the world. Almost all developed nations either have a presidential system or a half-presidential system," Erdogan said.

"Preparations for a new constitution must be bravely carried out (so that) we can present it to the people to decide upon."

Erdogan blamed four successive elections for slowing economic growth, increasing unemployment and keeping interest rates high.