DAMASCUS, Syria -- Turkey's president said Tuesday that his troops will establish a 20-mile-wide "safe zone" in northern Syria, adding that Turkey would seek logistic and financial assistance from the United States and other allies to create the zone.

The announcement by Recep Tayyip Erdogan came as the United Nations' new special envoy for Syria arrived in Damascus, his first visit to the war-torn country since he took over in January.

Erdogan told his ruling party legislators in Parliament that the zone would keep "terrorists out," protect civilians and stem the flow of refugees.

Erdogan and President Donald Trump discussed the issue in a telephone call late Monday that apparently aimed to ease tensions after the U.S. president tweeted a threat to Turkey warning of economic harm should Ankara attack U.S.-backed Kurdish forces in Syria.

Ankara considers the Kurdish forces in Syria terrorists aligned with a Kurdish insurgency within Turkey's own borders.

Erdogan said the two leaders reached an "understanding of historical importance."

In Damascus, Geir Pedersen, the new U.N. special envoy for Syria, said he hopes to have productive talks with Syrian officials. He spoke briefly to reporters upon his arrival at the Four Seasons hotel after driving from neighbouring Lebanon. The veteran Norwegian diplomat took over from Staffan de Mistura, who stepped down for family reasons after four years and four months of peace efforts that led nowhere.

"I hope we will have very substantial and productive talks and look forward to talking to you more after my discussions," Pedersen said. His office tweeted that he is looking forward to productive meetings in Damascus.

Syria has said it will co-operate with Pederson if he avoids the "methods" of his predecessor and commits to Syria's territorial integrity.

Nearly half a million people have been killed in the seven-year civil war in Syria and various U.N.-led peace efforts and indirect talks between the Syrian government and opposition in Geneva ended in failure.

Most recently, de Mistura was working on setting up a committee meant to draft a new constitution -- a key step in ending the country's civil war. He said objections from the Syrian government were holding up the committee's launch. In his farewell U.N. briefing last month, he said "an extra mile" is needed to form the committee because a list of participants submitted by Russia, Iran and Turkey is unacceptable to the United Nations.

Pedersen has served the U.N. in various roles including as special co-ordinator for Lebanon in 2007-2008. He was a member of Norway's team that negotiated the 1993 Oslo accords, which resulted in mutual recognition between the Palestine Liberation Organization and Israel, and was Norway's representative to the Palestinian Authority between 1998 and 2003.