The Pentagon, both Russia and the Syrian regime, has warned against attempting to manipulate the chemical attack site in Aleppo. Pentagon spokesman Sean Robertson said in a statement: "It is necessary to ensure that the Syrian regime does not take advantage of pretexts to undermine the ceasefire, Idlib.

"We warn Russia against manipulating the site of the attack and urge it to ensure the safety of the OPCW inspectors so that the allegations can be verified in a fair and transparent manner," the spokesman said.

The Pentagon demanded immediate detection of the presumed location by international inspectors, with the freedom to meet all concerned and the ability to gather evidence without hindrance.

The Syrian government and Russia accused opposition fighters of being behind the bombing, while opposition officials denied the use of chemical weapons, and accused the government of being responsible for the bombing of the northern city of Aleppo on Saturday. Damascus by trying to implicate them.

Politically, representatives of the Syrian government and the opposition, as well as Russia, Turkey and Iran, began a new round of talks in Astana, capital of Kazakhstan, for two days, centered on the fragile truce announced 10 weeks ago in Idlib, northern Syria.

The tour will discuss the situation in the vicinity of Idlib, the last stronghold of the opposition and armed factions in Syria, and will also focus on creating conditions for the return of refugees and displaced persons, as well as post-war reconstruction.

The United Nations will be represented by its Special Envoy to Syria, Staffan de Mistura, during his most likely meeting on the Syrian conflict before leaving office.

Russia, which supports the Syrian regime, and Turkey, which supports some opposition factions, announced last September an agreement on the establishment of a "demilitarized zone" around Idlib, but the truce is in jeopardy after the chemical attack in Aleppo, after which Russia launched raids on the buffer zone near Idlib.

The new round of talks in Astana is expected to conclude today, round 11 since Moscow began diplomatic efforts in early 2017. The United States has attended a number of previous rounds, but will not participate in the current meetings.

Colonel Sean Ryan, a spokesman for the US-led coalition, said US forces planned to set up observation posts in northern Syria to prevent state fighters "urging" the terrorist to flee from the center of the Euphrates valley to Turkey, in the north of the country. Ryan said these points would provide more transparency.

UN war crimes investigators demanded Syria yesterday to inform families of those who disappeared while in custody, including relatives, medical records and the remains of those who died or were executed during their detention.