Turkish Prime Minister Ahmet Davutoglu Wednesday slammed as "hypocritical" calls by some countries urging Ankara to open its borders to Syrian refugees while failing to demand Russia halts punishing air strikes.

Turkey is under mounting pressure to open its border to people fleeing a Russian-backed assault by the Syrian regime of President Bashar Assad in the north of the war-torn country.

Iran blames the failure of Syria peace talks on the participation of "terrorists", state media said Wednesday ahead of an international meeting to try to get the process back on track.

"What created problems at the recent Syria meeting in Geneva was not having differentiated between the opposition and terrorists," Deputy Foreign Minister Hossein Amir Abdollahian told U.N. envoy to Syria Staffan de Mistura by telephone, according to state broadcaster IRIB.

Germany hopes diplomatic talks on Syria it is hosting this week will agree to provide humanitarian relief to Aleppo and other cities besieged by Russian-backed regime forces, officials said Wednesday.

U.S. Secretary of State John Kerry and his Russian counterpart Sergei Lavrov will be among participants at talks in Munich on Thursday which could discuss suspended U.N.-brokered talks.

Syrian Kurdish separatists on Wednesday opened a representation in Moscow amid a push by the Kremlin to have them included in Syria peace talks despite Turkey's objections.

"This is a historical moment for the Kurdish people," Merab Shamoyev, chairman of the International Union of Kurdish Public Associations, said at the ceremony in an industrial neighborhood in southeast Moscow.

The United Nations on Tuesday urged Turkey to open its borders to tens of thousands of Syrians who have overwhelmed nearby emergency camps after fleeing a major government offensive.

The main border crossing north of Syria's second city Aleppo remained closed, forcing huge crowds including women and children to sleep in tents or in the open.

More than a million Syrians are living under sieges mostly enforced by regime forces five years into the war, a new NGO report said Tuesday, warning the crisis was "far worse" than the U.N. has admitted.

A joint project collecting data from a network extending deep into trapped Syrian communities came to the grim conclusion that inadequate U.N. reporting may also "inadvertently encourage the expansion of the Syrian government's 'surrender or starve' strategy."

A suicide car bombing killed nine people Tuesday at a police officer's club in the Syrian capital, a monitor said, in an attack claimed by the Islamic State group.

The Syrian Observatory for Human Rights said at least 20 people were also wounded in the Damascus blast, adding that policemen were among the dead and injured.

U.N. investigators on Monday accused Damascus of "extermination" in its jails and detention centers, saying prisoners were executed, tortured to death or held in such horrific conditions that they perished.

Over the past four and a half years, thousands of detainees have been killed while being held by different sides in Syria's brutal conflict, the U.N. commission of inquiry on Syria said in its latest report.

Around 30,000 Syrians are at the Turkish border after fleeing a Russia-backed regime offensive on the northern region of Aleppo, Turkish Prime Minister Ahmet Davutoglu said.

With his country facing mounting pressure to open its border, Davutoglu said the refugees would be admitted if need be, although Turkey should not be expected "to shoulder the refugee issue alone."

Turkish President Recep Tayyip Erdogan expressed anger over a U.S. official's visit to a Kurdish militia group controlling the Syrian town of Kobane, urging Washington to choose between Turkey and the "terrorists" there.

A delegation including senior U.S. diplomat Brett McGurk, special envoy to an international coalition fighting IS in Syria and Iraq, last week met members of the Kurdish People's Protection Units (YPG), a powerful militia that is in control of Kobane.