ANKARA - The deputy foreign ministers of Syria, Turkey, Iran and Russia will meet in April in Moscow, Turkish and Iranian officials said on Tuesday, building on contacts between Ankara and Damascus after years of hostilities during the Syrian war.

Encouraged by President Bashar al-Assad's ally Russia, Syrian and Turkish officials held meetings last year, in a move towards normalising ties between states on opposing sides of Syria's 12-year-long conflict.

But Assad this month ruled out any meeting with Turkish President Tayyip Erdogan until Turkey is ready to withdraw its military from northern Syria, deemed occupying forces by the Syrian president.

The situation on the ground in Syria would be discussed at the April 3-4 in Moscow, a senior Turkish official said.

"This meeting is expected to be a continuation of the ministerial-level meetings that began during the normalization process," the official said.

"However, since there will be no ministerial-level participation and the meeting will be at a technical level, significant decisions are not expected."

Officials at the Turkish foreign ministry were not immediately available for comment.

Russia hosted a meeting of the Syrian and Turkish defence ministers in December, since when the original tripartite talks have been widened to include Assad’s other ally Iran, which has publicly supported the rapprochement.

Turkey has sent forces into much of northern Syria during the war, and has backed the Syrian opposition.

A previously planned meeting of four countries' deputy foreign ministers scheduled in March was postponed.

A senior Iranian foreign ministry official confirmed the meeting in Moscow in the first week of April.

A Syrian source with knowledge of the talks confirmed that a meeting between the deputy foreign ministers would take place soon but did not specify a date.

Citing Russian Deputy Foreign Minister Mikhail Bogdanov, Russian state-owned news agency RIA reported on Monday that the deputy foreign ministers of Russia, Turkey, Iran and Syria may hold consultations in Moscow in early April.

Erdogan, who once called Assad a terrorist, is facing the biggest political challenge of his two-decade rule in May when Turks vote in what is expected to be a tight election.

(Reporting by Orhan Coksun and Huseyin Hayatsever in Ankara, Parisa Hafezi in Dubai and Maya Gebeily in Beirut; Writing by Tom Perry; Editing by Jonathan Spicer and Ed Osmond)