Russia has reacted angrily to "unacceptable" British and American suggestions that it is committing war crimes in Syria's bloody civil conflict.
Moscow warned that the comments could harm the US-Russia brokered ceasefire in Syria, as Boris Johnson visited a refugee camp in Turkey, near the Syrian border.
The Foreign Secretary's visit to the camp around 161km from Aleppo in Syria comes after angry exchanges at the United Nations over the latest offensive by the Russia-backed regime to take the beleaguered city.
Russia was accused by Britain and the US of barbarity and helping Syrian President Bashar al-Assad's regime "unleash a new hell" on the city but Moscow has hit back.
Kremlin spokesman Dmitry Peskov said Russia considers the tone of the criticism "unacceptable" and insisted "such rhetoric is capable of causing serious harm to the resolution process" in Syria.
Peskov told reporters that Russia was concerned that "terrorists" were using the ceasefire to "regroup, to replenish their arsenals and for obvious preparations to carry out attacks."
Meanwhile, the Syrian regime said the ceasefire is still viable and said it was willing to take part in a unity government but also claimed the West was supporting "terrorists" in the country.
Their comments come after British ambassador Matthew Rycroft joined his US and French counterparts in walking out of an emergency session of the UN Security Council on Sunday in a show of anger.
The meeting came after Johnson warned that Moscow would be guilty of committing war crimes if its warplanes were deliberating striking civilian targets.
Rycroft told the security council meeting in New York that it was "difficult to deny" that Assad's regime and its Russian allies were engaged in committing war crimes.
"After five years of conflict, you might think that the regime has had its fill of barbarity - that its sick bloodlust against its own people has finally run its course," he said.
"But this weekend, the regime and Russia have instead plunged to new depths and unleashed a new hell on Aleppo."
The UN special envoy on Syria, Staffan de Mistura, said the offensive to take the city had unleashed "unprecedented military violence" on its inhabitants, killing at least 213 civilians, many of them women and children.
He said there had been reports of the use of bunker-busting bombs and incendiary weapons which created "fireballs of such intensity that they light up the pitch darkness in Aleppo as if it were daylight".
Earlier, Johnson accused Russian president Vladimir Putin of "protracting" and called for an investigation into whether Russian forces were committing war crimes.
"Putin's regime is not only as it were handing Assad the revolver, he is in some instances firing the revolver himself," he said.