European Council President Charles Michel said on Monday that Europe must strengthen its defences and shift to a "war economy" mode to face the threat posed by Russia.
He said that for decades Europe had not invested enough in its security and defence.
While there had been strides since Russia invaded Ukraine, including by increasing military manufacturing capacity by 50 per cent, far more was needed, Mr Michel said.
He called on countries to enable investments in defence, including by considering changing the mandate of the EU lending arm, the European Investment Bank, to allow it to support the continent's defence industry.
Mr Michel urged EU countries to ensure Ukraine received what it needed on the battlefield, including by spending EU money on military equipment, and using profits from Russia’s frozen assets to buy weapons for Ukraine.
EU countries approved an agreement on Monday to increase the bloc's support for Ukraine's armed forces by €5 billion ($5.4 billion), amid warnings that Kyiv's forces need more resources to hold the line against a larger Russian army.
A $60 billion US aid package for Ukraine is being held up by Congress.
Mr Michel said Europe must take responsibility for its own security and not rely heavily on the support of countries such as the US.
"If we do not get the EU's response right and do not give Ukraine enough support to stop Russia, we are next," he said.
"We must therefore be defence-ready and shift to a 'war economy' mode.
"If we want peace, we must prepare for war."
