Russia and Iran criticized the U.N. chief's withdrawal of Tehran's invitation to the long-awaited peace conference on Syria, as delegates began to arrive in Switzerland for the talks.
Russian Foreign Minister Sergei Lavrov called U.N. Secretary-General Ban Ki-moon's unexpected, last-minute decision to bar Iran from the talks a mistake, but not a disaster.
Lavrov reaffirmed Russia's stance that Iran's presence was essential for the success of the talks. In Tehran, Iran's Foreign Ministry sharply criticized Mr. Ban's diplomatic turnaround, saying the U.N. chief only did so under immense pressure.
Expectations for a breakthrough are low. The peace conference began amid a report alleging Syrian President Bashar al-Assad's government has tortured and killed some 11,000 detainees.
A team of internationally renowned war crimes prosecutors and forensic experts said their report is based on thousands of photographs smuggled out of Syria by a military police photographer whose job included documenting deaths in Mr. Assad's jails.
They said the cache of 55,000 images showed bodies that revealed signs of starvation, beatings, strangulation and other abuses.
One of the former war crimes prosecutors who signed the report compared the images from Syria to the "industrial-scale killing" of Nazi death camps.
The talks set to begin Wednesday will include the first meetings between Mr. Assad's government and his opponents. About 40 countries will be represented at the peace conference.
Wednesday's meeting will give the delegations an opportunity to address the effort before the process shifts to talks Friday between only the Syrian sides and U.N.-Arab League envoy Lakhdar Brahimi.
The United States and Russia led the effort to organize the peace talks. The aim is to establish a transitional government, accompanied by a ceasefire and a commitment to allow full humanitarian access.