* Erdogan tells Mitchell U.S. must engage Hamas

* Hillary Clinton to visit Ankara next week

* Turkey hopes to resume Israel-Syria mediation

By Zerin Elci

ANKARA, Feb 26 (Reuters) - U.S. special envoy to the Middle East George Mitchell said on Thursday Turkey will play a "key role" in President Barack Obama's efforts to achieve peace in the Middle East.

Mitchell, in Ankara as part of a tour that will also take him to Israel and the West Bank, said Muslim Turkey's ties with Israel and Arab countries was an asset for Obama's promise to make Arab-Israeli peace a foreign policy priority.

"Turkey is a crucial ally of the United States and an important force for peace and security in the Middle East," Mitchell told reporters after meeting Turkish Prime Minister Tayyip Erdogan.

NATO member Turkey, Israel's closest ally in the Middle East, has played a major role as a mediator in the past, in particular in bringing Israel and Syria to indirect negotiations.

Erdogan told Mitchell Washington should engage Hamas if progress is to be made on peace in the Middle East, a Turkish government official who was present at the talks told Reuters.

The United States, Israel and the European Union, which regard Hamas as a terrorist organisation, have ostracised the militant group from peace efforts.

Erdogan's Islamist-rooted AK Party government has regular contact with the Islamist group, which rules the Gaza Strip, and has long said it is part of a lasting solution.

"Even though we do not approve Hamas' methods, Hamas should not be excluded from the peace process and should be integrated into the political system and the peace process," the official said.

On Wednesday, British Foreign Secretary David Miliband said talking to Hamas was the "right thing to do". Israel has said it will not deal with Hamas until it ends all violence, abides by existing peace agreements and recognises Israel's right to exist.

Turkey's fierce criticism of Israel's campaign in the Gaza Strip has soured ties between the two Middle East allies, but diplomats and analysts have said damage should be short-term.

Highlighting the U.S. desire to see Turkey engaged in Middle East peace efforts, U.S. Secretary of State Hillary Clinton is expected to visit Ankara next week in her first foray into Israeli-Palestinan peacemaking, officials said.

Ankara has been active in bridging a Palestinian rift between the Western-backed Palestinian Authority of President Mahmoud Abbas, which controls the occupied West Bank, and Hamas.

Turkish officials also told Reuters Ankara hopes to resume mediation between Israel and Syria once a new government is formed in Israel. Those talks collapsed after Israel's offensive in Gaza.

Mitchell was appointed last month to the post of U.S. Middle East envoy, responsible for Israeli-Palestinian negotiations. (Writing by Ibon Villelabeitia; editing by Angus MacSwan) (ibon.villelabeitia@reuters.com; Telephone: ++90 312 292 7022; Reuters Messaging: ibon.villelabeitia.reuters.com@reuters.net))

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