“We’ve sought to provide possible off-ramps to President Putin. He’s the only one who can decide whether or not to take them. So far, every time there’s been an opportunity to do just that, he’s pressed the accelerator and continued down this horrific road that he’s been pursuing,” Blinken said at a joint news conference with his British counterpart Liz Truss.

“He has a clear plan right now to brutalise Ukraine, but to what end?” Blinken said, adding that Ukrainians have shown that they would not accept any “puppet regime” that Putin might try to install to replace the elected Ukrainian government.

“If he tries to enforce such a puppet regime by keeping Russian forces in Ukraine, it will be a long, bloody, drawn-out mess,” Blinken said.

Senior US defence officials last month assessed that Russia’s invasion of Ukraine is designed to “decapitate” Ukraine’s government.

More than 2 million people have fled Ukraine since Putin launched the land, sea and air invasion on Feb 24. Moscow calls its action a “special military operation” to disarm its neighbour and dislodge leaders it calls “neo-Nazis”.

The war has swiftly cast Russia into economic isolation as well as drawing almost universal international condemnation. The United States on Tuesday banned imports of Russian oil, while Western companies are rapidly pulling out of the Russian market.

Russian forces hold territory stretching along Ukraine’s northeast border, the east and the southeast. Fighting has taken place on the outskirts of the capital Kyiv, while Ukraine’s second city, Kharkiv, is under bombardment.

Blinken has also slammed Russia for not allowing safe passage to civilians stuck in cities under heavy bombardment.

“The Kremlin’s proposals to create humanitarian corridors leading into Russia and Belarus are absurd,” he said.

Russia earlier this week had offered Ukrainians escape routes to Russia and its close ally Belarus, a proposal that a spokesperson for Ukrainian President Volodymyr Zelensky said was “completely immoral”.

(Reporting by Humeyra Pamuk and Daphne Psaledakis. Additional reporting by Susan Heavey. Editing by Chizu Nomiyama and Paul Simao.)