Two vital signals were given by the leaders of the European Union at their emergency summit on Friday. First, they spelled out their total solidarity with the US and the American people in the wake of the terrorist attacks in New York and Washington. Second, they ordered urgent and long overdue measures to make the struggle against terrorism more effective.

This should provide Washington with welcome reassurance that Europe sees the attacks not simply as an assault on America, but on all open, democratic, and multicultural societies. The response should be united, too. It should result in much closer and swifter co-operation than hitherto, both within Europe and across the Atlantic. That will require increased exchange of intelligence, greater trust between allies, and mutual support against terrorist threats.

It is essential that the EU should now show practical as well as moral solidarity in the struggle ahead. That means being realistic, not just rhetorical. It also means exploiting Europe's connections in building a broad international alliance against terrorism, including as many states as possible in the Arab and Muslim world.

Critical support

EU leaders are right to underline the importance of the United Nations Security Council resolution 1368 as legitimation for a US riposte to the attacks it suffered. Maintaining UN backing for action is going to be critical in uniting a truly global coalition against a lethal and elusive enemy. And ensuring that actions are carefully targeted, even when directed against states supporting or harbouring terrorists, is an essential part of that process.

Europe can complement the efforts of America in building the global coalition. The EU can use its links to countries such as Iran and Syria to ensure that they support the campaign as much as more obvious allies such as Egypt or Saudi Arabia. Such countries' reaction could be critical in denying terrorists a future safe haven, but they must be persuaded that the anti-terrorist actions are not going to be indiscriminate.

In practical terms of containing terrorism, the co-operation ordered by the EU leaders in their own backyards is likely to be just as important. Agreement on a common definition of terrorism is overdue. There have been too many squabbles over extradition. The logic of the EU must be that members trust each other to give an accused terrorist a fair trial.

Common warrant

The proposed tool to enable fast-track extradition is a common European arrest warrant. Negotiating such an agreement by December, as required by the EU leaders, is likely to prove well nigh impossible unless it is limited in the first place to those suspected of supporting or planning terrorist acts. This is not the moment to enact a single European judicial space in haste. It will be hard enough to ensure that in stepping up anti-terrorist measures, fundamental rights and freedoms remain guaranteed, as the summit rightly requires.

If the atrocities in New York and Washington can galvanise intelligence and counter terrorism agencies on both sides of the Atlantic to co-operate more closely, it will be a considerable achievement. The US has not trusted many European intelligence agencies to share its secrets in the past. On the one hand, European agencies need to prove they are secure. On the other, American counterparts have been over anxious to protect their technology and sources.

But if the Atlantic partners cannot trust each other, terrorists and their sympathisers will be the only ones to benefit from the ensuing confusion. This is a common struggle to defend universal values of tolerance, openness and justice. The challenge is to wage an unstinting war on global terrorism without harming those values. Force is unavoidable. But also essential are solidarity, trust, and the broadest possible coalition of allies.