Handout photo obtained from the Turkish Presidential Office shows U.S. Secretary of State Hillary Clinton speaking to Turkish Prime Minister Recep Tayyip Erdogan at the Turkish presidential office in Istanbul on Aug.11, 2012. (KAYIHAN OZER/AFP/GETTY IMAGES)

Secretary of State Hillary Rodham Clinton sought Saturday to broaden U.S. contacts with political opponents of Syrian President Bashar al-Assad beyond a fragmented group of exiles with limited influence inside the country.

The top U.S. diplomat also pledged more military and intelligence cooperation with Turkey, a close U.S. ally now receiving a daily tide of refugees from the 17-month conflict.

“We have been closely coordinating over the course of this conflict, but now we need to get into the real details of such operational planning,” Clinton said during a day of meetings with Syrian opposition figures, refugees and top Turkish officials.

“Our intelligence services, our military have very important responsibilities and roles to play so we are going to be setting up a working group to do exactly that,” she said.

Clinton and Turkish Foreign Minister Ahmet Davutoglu said they are planning for the worst-case scenario in Syria — all-out civil war, foreign terrorist infiltration and the possible use of Assad’s stockpile of chemical weapons.

“We have to brace for impact,” Davutoglu said.

Clinton came to Istanbul in part because it is a gathering place for Syrian opposition figures, including some who have recently arrived via a “corridor” of rebel-held territory south of the Turkish border.

The group she saw Saturday included Internet activists, student protesters and others who her advisers hoped could provide greater clarity about the true nature of the political opposition in the country.

While reluctant to criticize the outside political figures directly, U.S. officials are increasingly concerned that the umbrella Syrian National Council and other outside groups have limited leverage and competing agendas.

Clinton described the concern of one young man who she said plans to return to Syria. The man told her he was worried about “the apparent lack of unity among the outside opposition” and hoped the “opposition would rise to the occasion,” said Clinton, whose one-day stop here follows a 10-day trip to Africa.

A senior State Department official said the United States is seeking contacts with young people particularly, and with legal activists whose documentation of abuses could one day be used to hold Assad’s regime accountable.

The United States wants to see the external groups coalesce and “strengthen their connections on the inside,” said the official, who spoke on the condition of anonymity to describe the sensitive outreach.

Reporters were excluded from Clinton’s sessions with Syrian activists and refugees, but the State Department gave general descriptions of the participants.

One was described as a male member of the Syrian Center for Justice and Accountability, another a female “digital activist” affiliated with the Center of Civil Society and Democracy in Syria. The participants’ full identities were not disclosed to protect them from reprisals, according to the State Department.

Clinton did not directly address the debate within the administration and among allies about whether to consider a “no-fly zone” over Syria, like the one established with heavy U.S. involvement in Libya last year.

Clinton and Davutoglu said they had discussed a range of security issues including such a zone or “safe zones” within Syria or along the Turkish border.

“Sorting this out is what we have agreed to do,” Clinton said. “We have a long list.”

Clinton was clear that anything the United States agrees to do will be limited and in keeping with the view that adding arms to the volatile conflict could worsen it.

“We have to be careful,” she said.

The U.S. view, publicly articulated most recently by U.N. Ambassador Susan Rice on MSNBC on Thursday, is that a no-fly zone would be complicated and involve adding ground troops, something the Obama administration has thus far ruled out.

A no-fly zone would probably have to include U.S. air assets, although Turkish and other allied forces might be able to establish one on their own. No-fly zones have been applied to varying effect in Iraq and other countries, and generally involve regular air patrols by U.S.-allied warplanes equipped with missiles and backed by radar and other surveillance.

Militarily-protected safe zones are less clearly defined, and Davutoglu said that if the Syrian conflict gets significantly worse, safe zones for refugees might be a better option than continuing to try to care for them as they stream over the border.

Clinton also announced $5.5 million in new aid for refugees. More than 51,000 Syrians have sought refuge in Turkey. Many more have gone to Jordan, Lebanon and Iraq.