* U.S. has done "number of things" to support Syrian opposition
* Most of Syrian opposition not of "al Qaeda ilk"
WASHINGTON, Aug 8 (Reuters) - A senior aide to President Barack Obama did not rule out on Wednesday the eventual creation of a no-fly zone over a patch of Syria that increasingly appears to be controlled by anti-government rebels.
Some Republican critics of Obama's handling of the Syria crisis have been advocating international enforcement of a no-fly zone to prevent Syrian warplanes from operating over designated zones, as well as more directly arming the opposition forces fighting to overthrow President Bashar al-Assad.
The United States has so far declined to provide weapons directly to a fragmented opposition as U.S. officials say it is difficult to identify factions and who they represent. Instead, Washington has focused on humanitarian aid, communications gear and other non lethal support.
"The United States government always looks at situations and looks at what types of scenarios might unfold, and then accordingly looks at what types of contingency plans might be available to deal with certain circumstances," said John Brennan, Obama's senior counter-terrorism adviser.
"So rest assured that various options that are being talked about in the press, and sometimes being advocated, these are things that the United States government has been looking at very carefully, trying to understand the implications, trying to understand the advantages and the disadvantages," he said.
Asked during an appearance at the Council on Foreign Relations more pointedly about a no-fly zone, Brennan replied: "I don't recall the president ever saying that anything is off the table."
Brennan's remarks came as the Obama administration is incrementally increasing its backing for Syrian rebels, and accelerating planning for a post-Assad Syria.
Secretary of State Hillary Clinton is due to have talks on Syria in Turkey on Saturday. She said as recently as Tuesday that the rebels reportedly held territory from northern Aleppo, Syria's largest city, to the Turkish border.
Still, the United States sees few good options in the 17-month-old Syrian uprising and is wary of becoming involved in another military conflict as it seeks to leave behind wars in Iraq and Afghanistan.
"We have done a number of things in support of the opposition," Brennan said, without going into detail. "There is a lot of humanitarian assistance that is going in there. What we want to do is to make sure that we understand exactly who are going to be the recipients of any type of aid."
While al Qaeda will try to exploit the situation in Syria, "when you look at the Syrian opposition as a whole, the overwhelming majority of them are not of al Qaeda ilk. They are Syrians who are truly trying to gain control of their lives and their future," Brennan said.
DEFENDING YEMEN OPS
Brennan also defended U.S. counter-terrorism efforts in Yemen, where the use of drone strikes on suspected militants has raised criticism about the killings - including that of militant Anwar al-Awlaki, a U.S. citizen.
He said U.S. counter-terrorism efforts in Yemen are conducted in concert with the Yemeni government.
"And contrary to conventional wisdom, we see little evidence that these actions are generating widespread anti-American sentiment or recruits for AQAP," he said, referring to Al Qaeda in the Arabian Peninsula, the group's Yemen-based affiliate.
"In fact, we see the opposite. Our Yemeni partners are more eager to work with us. Yemeni citizens who have been freed from the hellish grip of AQAP are more eager, not less, to work with the Yemeni government," he said. "In short, targeted strikes against the most senior and most dangerous AQAP terrorists are not the problem, they're part of the solution."
On another topic, Brennan denounced recent leaks of sensitive national security information, and disputed critics who said that some of those leaks came from the White House itself to burnish Obama's image as commander in chief.
"There have been some devastating leaks," Brennan said without mentioning specific instances. "It's unconscionable what has gone out. The president has made his displeasure abundantly clear to his senior team" and that anybody responsible should be held accountable, he said.
Reuters reported in May that Brennan, in a private teleconference with former counter-terrorism advisers who are now TV commentators, may have unintentionally led to the public disclosure of a Western informant who helped thwart a new "underwear bomb" plot being planned by AQAP.