UN Syria mission to end, Russia calls meeting of key powers

* Russia regrets withdrawal of observers, calls NY meeting

* UN Syria mission to be replaced by small political office

* UN official: Both sides in Syria chose "path of war"

By Louis Charbonneau and Michelle Nichols

UNITED NATIONS, Aug 16 (Reuters) - The U.N. Security Council will not renew the mandate of a U.N. observer mission in Syria, which is due to expire in the coming days, and will begin its withdrawal from the country, French U.N. Ambassador Gerard Araud said on Thursday.

"The mandate of UNSMIS is over on the 19th of August ... UNSMIS will fade out," said Araud, who is the president of the Security Council for the month of August.

He said conditions for renewing the mandate of the observer mission, known as UNSMIS, had not been met.

Russian U.N. Ambassador Vitaly Churkin said the permanent Security Council members - Russia, China, the United States, France and Britain - and key regional players would meet on Syria in New York on Friday morning.

"We're sorry that the UNSMIS mandate is coming to an end," he told reporters. "We believe that those members of the council who insisted that UNSMIS can't continue, did not really show commitment to ending hostilities and to working toward a political settlement in Syria."

Russia had repeatedly called for the monitors to remain in Syria. But the United States opposes keeping them in the country as long as Syrian President Bashar al-Assad's forces continued to escalate their 17-month-old onslaught against an increasingly armed and determined opposition.

Moscow, with the aid of Beijing, has vetoed three resolutions criticizing and threatening sanctions against Syria. That has led to an impasse on the council, U.N. diplomats say.

The Security Council said last month it would only renew the mandate of the mission, which was deployed in April to monitor a truce that never took hold, if the world body confirmed a "cessation of the use of heavy weapons and a reduction in the level of violence by all sides sufficient" for it to operate.

In an Aug. 10 letter to the Security Council, U.N. Secretary-General Ban Ki-moon said this has not been achieved and the mission "has not been able to exercise its key functions of monitoring the cessation of violence."

Deputy U.N. peacekeeping chief Edmond Mulet told reporters that the mission's legal mandate would expire at midnight New York time on Sunday (0400 GMT) and the last military observers would be out of Syria by Aug. 24.

"It is clear that both sides have chosen the path of war, open conflict and the space for political dialogue and cessation of hostilities and mediation is very, very reduced at this point, but that doesn't mean we should not be engaged in that," Mulet told reporters after privately briefing the council.

"The situation on the ground is extremely difficult," he said. "But the fact that it's difficult doesn't mean that we should not face that challenge of trying to open those political spaces in the future."

The mission's initial 300 unarmed observers suspended most of their activity on June 16 because of increased risk from rising violence. UNSMIS now has over 70 civilian staff working issues such as aid access and monitoring human rights abuses.

Mulet said UNSMIS would be replaced with a U.N. political liaison office with 20 to 30 people, including military advisers and human rights, aid and de-mining experts.