U.S. Deputy Secretary of State William Burns visited Turkey to further press international sanctions against Iran over its controversial nuclear energy program. However, Ankara remains opposed to the new U.S.-led measures.

Turkey agreed to enforce United Nations measures against Iran, however, refusing to join other sanctions pushed by the U.S. and the European Union.

According to Turkish diplomatic correspondent Semih Idiz, Burns is the latest in a string of high-level American officials to visit Turkey.

"Turkey has made it clear it's against sanctions on Iran. So now we see Washington actively lobbying Turkey at the highest level. This adds pressure on Turkey, of course. But it doesn't resolve Turkey's dilemma of having to tread a cautious line between these two sides," said Idiz.

Ankara is pressing for a diplomatic solution to Iran's nuclear program. Turkish Foreign Minister Davutoglu said after visiting Tehran last week that Turkey could host an international gathering to resolve the crisis, Voice of America reported.