By Angela Dewan and Nic Robertson

CNN

LUCCA, Italy (CNN) -- Leading US allies have failed to reach agreement on new sanctions on Syria and Russia in the wake of a chemical attack that killed more than 80 people.

A meeting of G7 foreign ministers rejected a British plan to impose targeted sanctions on military personnel in Russia and Syria who had been "contaminated by the appalling actions of the Assad regime."

Britain had hoped to strengthen the hand of US Secretary of State Rex Tillerson ahead of his talks with Russian Foreign Minister Sergey Lavrov in Moscow.

Instead, the plan was shelved until after the results of an investigation into the attack on the rebel-held town of Khan Sheikhoun last week, which prompted the US to launch a barrage of missiles on a Syrian airbase on Friday.

"There is no consensus on additional new sanctions," Italian Foreign Minister Angelino Alfano said.

Speaking after the meeting, Tillerson denounced Russia's "failure" to ensure the elimination of chemical weapons in Syria and said it had not made enough progress in peace talks.

Tillerson said that Russia had failed to uphold commitments it made in 2013 to guarantee the Syrian regime got rid of chemical weapons..

"These agreements stipulated Russia, as the guarantor of a Syria free of chemical weapons, would locate, secure, and destroy all such armaments in Syria. Stockpiles and continued use, demonstrate that Russia has failed in its responsibility to deliver on its 2013 commitment," he said.

"It is unclear whether Russia failed to take this obligation seriously or Russia has been simply incompetent in its ability to deliver on its end of that agreement."

Ultimatum for Moscow

But he also laid down an ultimatum for Russia, saying that Moscow must think about whether to remain an ally with the Assad regime, the Iranians and Hezbollah.

"Is that a long term alliance that serves Russia's interests? Or would Russia prefer to realign with the United States, with other Western countries and Middle East countries that are seeking to resolve the Syrian crisis?"

He also said that Russian-brokered talks in Astana had "not produced much progress," adding that he had hope that a process underway in Geneva over Syria's political future would be fruitful.

"And our hope is Bashar al-Assad will not be part of that future," he said, without explicitly calling for Assad's removal.

"In terms of the future of Bashar al-Assad, it is important to us that we undertake a political process that leads to the final conclusion of how Syria will be governed. It is our policy for a unified Syria that is governed by the people of Syria. I think it is clear to all of us that the reign of the Assad family is coming to an end," he said.

CNN's Joseph Netto and Judith Vonberg contributed to this report.