Russia challenged President Trump on Thursday to lay out his strategy on how he will respond to Syrian leader Bashar al-Assad after Trump declared the poison gas attacks against civilians “crossed a lot of lines,” according to a report.

“Russia’s approach to Assad is clear. He is the legal president of an independent state. What is the US approach?” Russian Foreign Ministry spokeswoman Maria Zakharova told CNN in a text message.

Trump, in a Rose Garden press conference Wednesday after meeting with Jordan’s King Abdullah II, called the attack that killed at least 86 people, including women and children, a “terrible affront to humanity.”

“My attitude toward Syria and Assad has changed very much. The attack on children had a big impact on me,” Trump said.

Asked how he would respond, the president said he wouldn’t divulge his plans, saying, “You’ll see.”

Moscow, which has been backing the Syrian government in its fight against “terrorist aggression” from the Islamic State since September 2015, said the gas leaked from a rebel arms depot after the site was struck by Syrian warplanes.

Syria blamed the attack on terrorists.

At an emergency meeting of the UN Security Council on Wednesday, Ambassador Nikki Haley said if the global body fails to take action, “We may.”

“Time and time again, Russia uses the same false narrative to deflect attention from their allies in Damascus. How many more children have to die before Russia cares?” she said.

The US, France and Britain have proposed a draft UN resolution condemning Syria for the attacks.

But Russia’s Foreign Ministry said the resolution was based on “fake news” and Moscow would veto it.