US Secretary of State John Kerry has called on the international community to try Russian President Vladimir Putin for alleged “war crimes”.

As diplomatic relations between Russia and the U.S. continue to deteriorate, a defiant Kerry intensified the tensions by calling for a war crimes probe of Moscow’s fight against ISIS in Syria.

“Russia and the regime owe the world more than an explanation about why they keep hitting hospitals, medical facilities, children, women,” Kerry told reporters after meeting with the French Foreign Minister Jean-Marc Ayrault on Friday.

“These are acts that beg for an appropriate investigation of war crimes.” Kerry called the actions of the Syrian military and the Russian air force “beyond accidental” and “a targeted strategy to terrorize civilians.”

Rt.com reports:

Kerry prefaced his remarks about “war crimes” by claiming that the Syrian forces hit “another hospital” in Aleppo overnight, killing 20 people and wounding 100. There has been no confirmation of the attack, whether from government or rebel sources.

Syrian jets, backed by the Russian air force, are targeting militants in East Aleppo after jihadist groups in control of the enclave there repeatedly violated the cessation of hostilities, according to Moscow and Damascus.

UN estimates put the number of militants in East Aleppo between six and eight thousand, said Russian Foreign Minister Sergey Lavrov, about half of whom belong to the terrorist organization Al-Nusra Front. Russia is prepared to urge the Syrian government to let them depart the city, Lavrov added.

UN’s envoy for Syria, Staffan de Mistura, personally offered to escort the militants out.

“If you [Al-Nusra] did decide to leave, in dignity with your weapons, to Idlib or anywhere you wanted to go, I personally am ready, physically ready, to accompany you,” he said on Thursday.

Washington suspended bilateral contacts with Russia over the Syrian crisis on Monday, accusing Moscow of not doing enough to restrain the government in Damascus. The Foreign Ministry in Moscow said that Russia had made every effort to preserve the September 9 ceasefire agreement, while repeatedly urging Washington to live up to its obligations and separate the so-called “moderate opposition”fighters from Al-Nusra and other terrorists.

Kerry’s remarks come as the Syrian Army made advances in the Sheikh Saeed district of Aleppo, on the southern side of the rebel-held enclave. Even as government bombardment has lessened, shelling from the rebel side killed 11 people in the government-held Al-Jamaliyeh neighborhood on Thursday. Authorities in Damascus have said “there is no other option” but to continue to fight the rebels until they leave Aleppo.