Turkish Officials to Boycott Meetings with US Ambassador: Erdogan

"The document testifies to the readiness of the two educational institutions to develop cooperation in the educational sphere, promotes the exchange of scientific experience and the development of educational programs", the press service said.

Total trade between Serbia and Turkey should reach $1.2 billion (1 billion euro) in 2017, RTS quoted Erdogan as saying during a business forum in Belgrade organised within the framework of his official visit to Serbia.

In the Serbian capital, Erdogan held talks with Serbian President Aleksandar Vucic that focused on trade and investment, but also touched on political relations in the region.

The Turkish restrictions appeared to go further than a move by the U.S. to suspend the processing of "non-immigrant" visas, a specific category that relates to tourism, medical treatment, business, temporary work or study.

Relations between Serbia and Turkey have improved in recent years after decades of mistrust between the two nations.

Turkey backed Bosnian Muslims in the 1990s war that pitted them against the Christian Orthodox Serbs and Catholic Croats. Serbia was ruled for nearly 500 years by the Ottoman Empire.

"But, I have the courage to say I will work in the interest of all nations", he said.

President Erdogan Tuesday sought to personally blame U.S. Ambassador John Bass for the tensions. A banner in Novi Pazar on Wednesday showed Gulen dressed in a prison uniform.

But the State Department said that Bass had been operating with the full authority of the USA government.

"Of course, the implementation of our goals will be facilitated, inter alia, by the arrangement of a special communications line, which has recently been set up between the presidents of Ukraine and Turkey", Poroshenko said. "We will preserve our friendship".