US President Donald Trump on Wednesday tweeted that Russian Federation shouldn't be allied with a "Gas Killing Animal", in reference to Assad whose regime is accused of carrying out the attack on Douma, which activists and rescuers say killed at least 40 people.
Syria's letter came hours ahead of a UN Security Council meeting on rival proposals by Russian Federation and the U.S.
"Even if he (Trump) fires what he calls smart bombs, at us they will be stupid bombs because they will backfire on him and Syrians will be stronger", al-Issa said.
"On a strategic level, it's how do we keep this from escalating out of control, if you get my drift on that", he said. But Moscow remains alone because leaders of Western countries have taken the side of the United States, announcing that they will join it if it made a decision to attack the Assad forces directly. Syria's official SANA news agency reported.
Douma was the last part of the rebel enclave on the eastern edge of Damascus to escape government control.
Moscow and Washington blocked attempts by each other at the United Nations Security Council on Tuesday to set up worldwide investigations into chemical weapons attacks in Syria.
The drumbeat of military action appeared to grow louder, as Russian Federation stonewalled diplomatic efforts at the United Nations and France declared "proof" that Moscow's Syrian ally carried out a deadly chemical weapons attack that killed more than 40 Syrians.
The Syrian president added that the threats endanger global peace and security and that military action would only contribute to the "further destabilization" of the region.
Moscow and the Syrian regime deny that the gas attack took place or that either regime was involved.
In London, British Prime Minister Theresa May summoned her Cabinet back from vacation Thursday to discuss military action against Syria.
Possible strikes in Syria have been the forefront of discussion since an attack last weekend that killed dozens and injured hundreds in Douma, a town in the Damascus suburb of Eastern Ghouta.
But while the Russian president's lieutenants continued to up the ante with threats and allegations, Vladimir Putin himself adopted a more statesmanlike tone, in remarks to new ambassadors presenting their credentials at the Kremlin.
But a special hotline for the U.S. and Russian militaries to communicate about operations in Syria is active and being used by both sides, Moscow said Thursday. "It's possible two or three (more) days", he said.
Russia, which backs Mr Assad, has softened its initial threats to retaliate against U.S. ships and bases in event of an attack.
Mr Hamadmad and his family fled Syria when it was under the government of Hafez al-Assad, father of current President Bashar al-Assad. While UK Prime Minister Mrs May isn't required to seek parliamentary approval, it's accepted that lawmakers will have a say before committing military forces.
"Perpetrators of such attacks must be identified and held accountable", the U.N.'s International Commission of Inquiry on Syria said in a statement, noting that the use of such weapons is strictly banned under a global treaty ratified by Syria.
"We should all be outraged at these horrific reports and images from Douma" where Saturday's attack took place, said Peter Salama, the United Nations agency's chief of emergency response.
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