VOULIAGMENI, Greece  -- Turkish Prime Minister Recep Tayyip Erdogan on Friday promised closer cooperation with EU neighbor Greece to fight illegal immigration into Europe in exchange for Greek assistance to help relax visa rules for Turks.

Erdogan is visiting Greece for the second time in five months, as the two countries seek to boost trade and sideline their traditional rivalry.
"On (immigration) we will start cooperation so that we can deal with this problem ... it is a common problem," Erdogan said after a two-hour meeting with Greek Prime Minister George Papandreou on the fringes of a Mediterranean climate change conference near Athens.

Greece is the European Union's busiest transit point for illegal immigration and has faced a spike in recent months in clandestine traffic across its 125-mile land border with Turkey.

Greek officials have long accused authorities in Turkey of failing to make a determined effort to stop immigrants sneaking into Greece and of ignoring an agreement to accept the return of detained migrants.

Papandreou said Greece and Turkey had agreed to "reactivate" that agreement.

"We decided on a common initiative toward the EU ... to make our cooperation more systematic and much more effective in dealing with this problem," he said.

"At the same time, we discussed the very important issue of liberalizing the visa process for Turkish citizens entering the European Union."

NATO allies Greece and Turkey have improved ties over the past decade but remain at odds over war-divided Cyprus and boundaries in the Aegean Sea. The disputes have hindered Turkey's bid to join the European Union.

Papandreou said the two leaders had discussed the course of efforts to resolve those disputes "in a very positive atmosphere."

And Erdogan described as "very significant" a recent decision by his government to grant Turkish citizenship to 12 senior clerics at the Ecumenical Patriarchate in Istanbul, the center of Orthodox Christianity around the world.

Clerics must have Turkish citizenship to be able to succeed the current Ecumenical Patriarch, 70-year-old Bartholomew I.

On Thursday, NATO's secretary general Anders Fogh Rasmussen said on a visit to Athens that Greece and Turkey were showing a greater willingness to cooperate.
"I appreciate very much the close contact, as I see it, that we are now witnessing between Ankara and Athens," the NATO chief said.

"I think Prime Minister Erdogan's visit to Athens ... is yet another testament to the improvement of relations, and we appreciate that very much."

Leaders and representatives from 16 Mediterranean countries are attending the meeting at the seaside resort of Vouliagmeni, south of Athens, also joined by environmental campaigners and representatives of the World Bank and European Investment.

Papandreou said Mediterranean countries were "particularly vulnerable" to global warming -- facing more frequent droughts, heatwaves and forest fires -- and said he was encouraged by Erdogan's presence at the conference.

"This is proof that two neighbors can place their differences to one side to face common threats," he said, in his opening remarks earlier Friday.

The conference ends Saturday.