Syria's foreign minister said Friday it was premature to talk of direct peace negotiations with Israel, a day after Israel had called for quickly starting face-to-face discussions.

A third round of talks between the long-time foes started in Istanbul on Tuesday and ended on Thursday with an agreement to hold a fourth round of indirect negotiations in Turkey in late July, a Turkish government source said Thursday.

"It's premature to answer this question," said Walid al-Moualem when asked when direct talks could be held.

"The moment when we feel that we've got the agreed common ground between us and the Israelis, which covers all elements of a peace agreement, we will agree on the location of these direct talks," he said in a question and answer session at the French Institute for International Relations (IFRI).

"The direct talks need an active American participation and sponsoring. To give guarantees we need an active European role maybe represented by France. We need also a role for Russia, a role for the United Nations for these talks," he said.

The latest round of indirect negotiations between Israel and Syria covered core issues including the future of the Golan Heights, Army Radio reported on Friday, quoting a Turkish official.

As Israel and Syria approach a fourth round of Turkish-mediated peace talk, Jerusalem will demand Damascus prove its readiness to sever its Iranian ties and condemn terror, the radio said.

Senior government officials Shalom Turgeman and Yoram Turbowicz, who are charged with conducting the negotiations on behalf of the Prime Minister's office, returned to Israel from Turkey on Thursday following two days of indirect talks.

The two said despite the progressing negotiations, there remain significant rifts between the Israeli and Syrian positions, the radio said.

Prime Minister Ehud Olmert said on Thursday that the peace talks, now mediated by Turkey, would have to be conducted face-to-face "very soon."

"With the Syrians, we are talking seriously and in my estimation very soon the negotiations will have to be direct. They will not be able to continue in the mode in which they are currently being held," Olmert told an economic conference in the southern resort city of Eilat.

Olmert made his comments as the third round of indirect talks between Israel and Syria came to a close in Turkey on Thursday.

A Turkish government source said that Israel and Syria have agreed to hold a fourth round of indirect talks in late July. During that meeting, the sides will decide whether to move to direct talks starting in August, the source said.