ANKARA (Reuters) -- US Secretary of State John Kerry said on Friday the United States found a comment by Turkey's prime minister, likening Zionism to crimes against humanity, "objectionable", overshadowing their talks on the crisis in neighboring Syria.

Kerry, on his first trip to a Muslim nation since taking office, met Turkish leaders for talks meant to focus on Syria's civil war and bilateral interests from energy security to counter-terrorism.

But the comment by Turkish Prime Minister Tayyip Erdogan at a UN meeting in Vienna this week, condemned by his Israeli counterpart, the White House and UN Secretary-General Ban Ki-moon, has clouded his trip.

"We not only disagree with it, we found it objectionable," Kerry told a news conference with Turkish Foreign Minister Ahmet Davutoglu, saying he raised the issue directly with Davutoglu and would do so with Erdogan.

Kerry said Turkey and Israel were both key US allies and urged them to restore closer ties.

"Given the many challenges that the neighborhood faces, it is essential that both Turkey and Israel find a way to take steps in order to bring about or to rekindle their historic cooperation," Kerry said.

"I think that's possible but obviously we have to get beyond the kind of rhetoric that we've just seen recently."

Washington needs all the allies it can get as it navigates the political currents of the Middle East, and sees Turkey as the key player in supporting Syria's opposition and planning for the era after President Bashar Assad.

But the collapse of Ankara's ties with Israel have undermined US hopes that Turkey could play a role as a broker in the broader region.

Erdogan told the UN Alliance of Civilizations meeting in Vienna on Wednesday: "Just as with Zionism, anti-Semitism and fascism, it has become necessary to view Islamophobia as a crime against humanity."

Erdogan's caustic rhetoric on Israel has in the past won applause from conservative supporters at home but raised increasing concern among Western allies.

Ties between Israel and mostly Muslim Turkey have been frosty since 2010, when Israeli marines killed nine Turks in fighting aboard a Palestinian aid ship that tried to breach Israel's blockade of the Gaza Strip.

"If we must talk about hostile acts, then Israel's attitude and its brutal killing of nine of our civilian citizens in international waters may be called hostile," Davutoglu said, adding Turkey had always stood against anti-Semitism.

"No single statement carries a price higher than the blood of a person ... If Israel wants to hear positive statements from Turkey it needs to reconsider its attitude both towards us and towards the West Bank," he told the news conference.

Turkey has demanded a formal apology for the 2010 incident, compensation for victims and their families and for the Gaza blockade to be lifted. Israel has voiced "regret" and has offered to pay into what it called a "humanitarian fund" through which casualties and relatives could be compensated.

Support for Syrian opposition

Turkey's relations with the United States have always been prickly, driven more by a mutual need for intelligence than any deep cultural affinity. And Erdogan's populist rhetoric, sometimes at apparent odds with US interests, is aimed partly at a domestic audience wary of Washington's influence.

But the two have strong common interests. Officials said Syria would top the agenda in Kerry's meetings with Erdogan and President Abdullah Gul, building on the discussions in Rome between 11 mostly European and Arab nations within the "Friends of Syria" group.

After the Rome meeting, Kerry said on Thursday the United States would for the first time give non-lethal aid to the rebels and more than double support to the civilian opposition, although Western powers stopped short of pledging arms.

"We need to continue the discussion which took place in Rome ... in terms of the main goals there is no daylight between us and the Americans," a senior Turkish official said.

"A broad agreement was reached on supporting the opposition. Now our sides need to sit down and really flesh out what we can do to support them in order to change the balance on the ground," he said.

Turkey has been one of Assad's fiercest critics, hosting a NATO Patriot missile defense system, including two US batteries, to protect against a spillover of violence and leading calls for international intervention.

It has spent more than $600 million sheltering refugees from the conflict that began almost two years ago, housing some 180,000 in camps near the border and tens of thousands more who are staying with relatives or in private accommodation.

Washington has given $385 million in humanitarian aid for Syria but US President Barack Obama has so far refused to give arms, arguing it is difficult to prevent them from falling into the hands of militants who could use them on Western targets.

Turkey, too, has been reluctant to provide weapons, fearing direct intervention could cause the conflict to spill across its borders.