European Union justice ministers have agreed to begin negotiations with the United States for improved cooperation on extradition and investigations. However, diplomats say differences over some issues may hamper the talks.

The justice ministers, meeting in Luxembourg Friday, were acting on a pledge made after the September 11 attacks in the United States.

While the desire for improved cooperation is there, diplomats say differences over the use of capital punishment, life imprisonment without parole, U.S. military tribunals to try foreign terrorist suspects, and data protection would be stumbling blocks.

Danish Justice Minister Lene Espersen, who will lead the EU negotiations, expects tough talks on some issues. "What is really important at the moment is that the mandate is extremely broad, covers a lot of areas," Ms. Espersen said. "And, as I'm sure our American colleagues are well aware, we have strong reservations with regard to the death penalty. We want reassurances with regard to the fundamental rights and freedoms. And this means that it will be pretty tough negotiations with regard to the more principle matters, then on he overall level."

Minister Espersen says she hopes the sides will be able to establish joint investigation teams, and come to some sort of agreement on extradition. However, diplomats say the text of the justice ministers' agreement reached in Luxembourg would not accept any extradition treaty that allowed the United States to apply capital punishment to any suspect handed over.

Analysts say an EU-U.S. deal on extradition would be better than 15 bilateral agreements - if all EU member states agreed to extradite their own nationals.

An EU official says the European Union hopes to start talks with United States as soon as possible, so that a deal can be in place before the end of this year.