The EU should quickly set up a body to oversee the training of imams and ensure their messages to Muslim followers do not contribute to spreading an "ideology of hatred", the President of the European Council said on Monday.
Charles Michel was in Vienna with Austrian Chancellor Sebastian Kurz, a day before he will attend a video conference on the European response to terrorism, organised by French President Emmanuel Macron.
Europe has suffered two terrorist attacks over the past 10 days in the Austrian capital Vienna and the French city of Nice.
"To fight the ideology of hatred, we need to set up as soon as possible a European institute to train imams in Europe," Mr Michel, who heads the council of the EU's 27 heads of government, said on Twitter.
"Online messages glorifying terrorism must be quickly removed. There must be no impunity for terrorists and those praising them on the internet."
On Monday, Mr Michel and Mr Kurz stood in front of candles during a ceremony at the site of the extremist attack in Vienna.
Mr Kurz said that the EU needed to work together to stop foreign terrorists.
“[We need] a robust, co-ordinated approach against foreign terrorist fighters," he said.
"There are thousands of people who tried to leave Europe in the past couple of years in order to murder in Syria, Iraq or somewhere else.
“Some have returned, some were arrested by the authorities and couldn’t leave to begin with.
"But they had the idea to commit murder in Syria and Iraq. Some are still in prison but others are already free again. These people are ticking time bombs.”
Mr Kurz, a longtime critic of mass immigration, also called for proper protection of the EU’s external borders.
On Friday, EU interior ministers will hold a regular meeting in which they are expected to discuss Covid-19, the recent attacks and new measures to prevent them.
Dawn raids on Monday against groups suspected of operating on behalf of the Muslim Brotherhood and Hamas were carried out by Austrian police in a major crackdown.
Officers made 30 arrests in more than 60 raids under anti-terrorism laws, the Austrian government said.