ANKARA, April 16 (Reuters) - Turkey said on Thursday it would continue supporting peace talks between the United States and Iran and called on the sides to be "constructive" in negotiations to end the war.

Turkey, a NATO member and neighbour of Iran, has been in close touch with the U.S., Iran, and mediator Pakistan and has repeatedly called for fighting to stop.

"We will continue to provide the necessary support for the ongoing ceasefire to turn into a permanent truce and eventually lasting peace, without becoming more complex and difficult to manage," the Turkish Defence Ministry said at a weekly briefing.

Ankara hopes "the parties will be constructive in the ongoing negotiation process," it said.

U.S. and Iranian officials were weighing a return to Pakistan for further talks as early as the coming weekend, after negotiations ended on Sunday without a breakthrough.

A Turkish diplomatic source has said foreign ministers from Turkey, Pakistan, Saudi Arabia, and Egypt will meet on the margins of a diplomacy forum in the southern Turkish province of Antalya at the weekend. Pakistan's Prime Minister Shehbaz Sharif is also due to attend.

(Reporting by Tuvan Gumrukcu; Editing by Jonathan Spicer)