EU chief Ursula von der Leyen on Friday said Brussels would not pay to build barriers on the bloc's borders to keep out migrants, despite demands from a string of countries.
Von der Leyen, head of the EU's executive, said she told leaders at a summit in Brussels there was a long-standing position "that there will be no funding of barbed wire and walls".
A number of EU member states facing influxes on their borders have ramped up pressure for the bloc to use its budget to finance barriers.
Leading the way have been Poland and Lithuania as they scrambled to deal with a surge of illegal crossings from neighbouring Belarus.
The EU accuses Minsk of sending across thousands of migrants from the Middle East and Africa in retaliation for sanctions on the regime of President Alexander Lukashenko over his crackdown on opponents.
"We consider the behaviour of the Belarus government as a hybrid attack," von der Leyen told journalists.
The leaders agreed to hit back at Minsk with more sanctions "as a matter of urgency", the official conclusions from the summit said.
"Lukashenko's regime, now they'll see that the European Union is able to react, is able to take the decisions, and is ready to defend itself," Lithuanian President Gitanas Nauseda said.
Poland has drawn criticism for its hardline approach to the crisis that has seen guards push back migrants on the border.
The United Nations on Friday demanded urgent action to save lives and avoid suffering on the EU-Belarus border, following the deaths of several asylum seekers.
UNHCR, the UN Refugee Agency, said another fatality this week meant there had now been eight deaths along the border between Belarus and its European Union neighbours Latvia, Lithuania and Poland.
Warsaw has proposed building a 350 million euro ($410 million) wall on its border with Belarus.