European Union leaders warned Iran and Syria Friday against meddling in the affairs of their neighbors and demanded they adopt more "responsible" stances if they hope to improve ties with the bloc.

"The European Council expresses its concern about the negative impact of Iranian policies on stability and security in the Middle East," EU heads of state and government said in conclusions from their Brussels summit.

"The European Council underlines that Iran needs to play a responsible role in the region."

They expressed regret that, in the dispute over its nuclear program, Iran had rejected a package of incentives in exchange for stopping its enrichment of uranium, and encouraged the United Nations Security Council to take action.

And they denounced a conference on the Holocaust in Tehran this week that presented Nazi Germany's systematic slaughter of six million Jews during World War II as a matter of historical debate.

"The EU condemns any denial of the Holocaust as a historical fact, either in whole or in part," the leaders wrote.

On the latest political crisis in Lebanon sparked by anti-government protests organized by the Iranian- and Syrian-backed militia Hezbollah, the EU pressed the country's neighbors not to meddle in Lebanese affairs.

"The European Council calls upon all Lebanese and regional actors to show responsible leadership and full respect for Lebanese democratic institutions," they wrote.

"Syria must end all interference in Lebanese internal affairs and actively engage in the stabilization of Lebanon and the region. Syria needs to do so to be in a position to develop normal relations with the international community, including with the EU."

Opposition Shiites and Christians launched mass street protests December 1 in a bid to topple the Western-backed government.

The bloc is divided over how to contend with Syria, recognizing it is key to resolving the crises in Lebanon, Iraq and between the Israelis and the Palestinians.

German Foreign Minister Frank-Walter Steinmeier traveled to Damascus this week for talks with President Bashar al-Assad and held out the prospect of economic incentives if Syria became a "constructive" partner in the region.

But EU heavyweights such as France have ruled out negotiations until Syria demonstrates a significant turnabout in policy.

Germany will assume the rotating presidency of the bloc January 1 and has pledged to revive the Middle East Quartet grouping the EU, the UN, the United States and Russia.

The leaders encouraged the Quartet to "stand ready to lead an effort by the international community to build on the outcome of successful negotiations between Israel and the Palestinians".

They said this should entail a "comprehensive settlement" of the Israeli-Arab conflict, including peace agreements with Syrian and Lebanon and full normalization of relations between Israel and Arab countries.

And they called for an international conference "in due course" to realize those goals in consultation with the parties.