Britain's top diplomat called Wednesday for Western allies to send tanks, warplanes, and other heavy weapons to Ukraine, saying fears of escalating the war were misplaced and "inaction would be the greatest provocation."

Foreign Secretary Liz Truss said "this is a time for courage, not caution" among nations helping Ukraine fight Russia's invasion.

"Heavy weapons, tanks, airplanes — digging deep into our inventories, ramping up production. We need to do all of this," Truss said during an annual foreign policy speech at Mansion House, the residence of the Lord Mayor of London.

NATO nations have supplied Ukraine with military weapons and gear, including missiles, and armored vehicles. But they have been reluctant to send fighter planes — despite pleas from Ukrainian President Volodymyr Zelenskyy — for fear of escalation. Russian Foreign Minister Sergey Lavrov has already accused NATO of effectively waging a proxy war against Russia.

Western officials deny that, saying the conflict is between Russia and Ukraine due to Russia's illegal invasion of its neighbor.

Britain has sent 450 million pounds in military aid to Ukraine, including thousands of missiles. But Despite Truss's call for jets, British Prime Minister Boris Johnson's spokesman, Max Blain, said there were "no plans" for the U.K. to send planes. He did not rule out Britain sending planes to another country, such as Poland, that would then give its own jets to Ukraine, but said there were "no specific plans" to do so.

Truss said Russia's attack on Ukraine must be a wake-up call for international institutions that failed to prevent the invasion.

"The architecture that was designed to guarantee peace and prosperity has failed Ukraine," Truss said. "The economic and security structures developed after the Second World War and then the Cold War have been bent out of shape so far that they have enabled rather than contained aggression."

Truss called Russian President Vladimir Putin a "desperate rogue operator" who was ripping up the global order and outfoxing international institutions.

"Russia is able to block any effective action in the U.N. Security Council," where it has a veto as a permanent member, she said, adding that the Group of 20 club of wealthy and emerging nations "cannot function as an effective economic body while Russia remains at the table."

In response, Truss called for a new focus on "military strength, economic security and deeper global alliances" among "free nations."

After years of declining military spending in many countries, including Britain, she said NATO's goal that countries spend 2% of gross domestic product on defense should be "a floor, not a ceiling."

Truss also called for tougher economic sanctions on Russia, saying the West must cut off Russian oil and gas imports "once and for all." That would be an easier thing to do for Britain than for many other European nations.

"If Putin succeeds, there will be untold further misery across Europe and terrible consequences across the globe," she said. "We would never feel safe again. So we must be prepared for the long haul and double down on our support for Ukraine."