Defense Secretary Leon Panetta says plans to set up a no-fly zone over parts of Syria are "not on the front burner," despite persistent calls from rebel forces there that they need the added protection from escalating regime airstrikes.

In an interview with The Associated Press on Monday, Panetta said he is confident the U.S. could successfully enforce a no-fly zone over Syria, but doing so would require a "major, major policy decision" that has not yet been made.

"We have planned for a number of contingencies that could take place and one of those possible contingencies is developing a no-fly zone. But we've also pointed out difficulties in being able to implement that," Panetta said. "It's not on the front burner as far as I know."

Secretary of State Hillary Rodham Clinton said recently that Washington and Turkey are discussing a range of steps, including a no-fly zone over some parts of Syria. Rebel leaders have expressed frustration that the United States has limited its assistance to non-lethal aid.

The U.S. and its NATO allies successfully enforced a no-fly zone over Libya last year, as rebels there made gains and eventually ousted dictator Moammar Gadhafi. Syria, however, has relatively modern air defenses that are far more plentiful and sophisticated than those in Libya. Syria buys its arms from Russia and is backed in its efforts to tamp down the rebels by Iran.

Syrian President Bashar Assad's military has significantly stepped up aerial attacks in recent weeks, using missile strikes to push back opposition forces in key fronts such as Aleppo. Civil war has spread across the country, and activists say more than 20,000 people have been killed since the revolt against Assad began in March 2011.

Currently, Panetta said, the U.S. is focused on ensuring chemical and biological weapons there are secure and on providing humanitarian and non-lethal assistance to the rebels.

Panetta, 74, spoke at length on a number of topics during the AP interview in his Pentagon office, with his golden retriever, Bravo, lying at his side and playing with a red stuffed lobster toy.

Panetta revealed that Pakistan has told U.S. military officials that it plans to launch combat operations against Taliban militants soon in a tribal area near the Afghan border. The North Waziristan region serves as a haven for leaders of the al-Qaida-linked Haqqani network.

Pakistan's military chief, Gen. Ashfaq Parvez Kayani, discussed the planned operation with the top American commander in Afghanistan, Gen. John Allen, Panetta said, adding that he understands that it will begin in the "near future."

And while he welcomed the operation, he noted that the main target will be the Pakistani Taliban, rather than the Haqqani network.

"They've talked about it for a long time. Frankly, I'd lost hope that they were going do anything about it. But it does appear that they in fact are going to take that step," Panetta said.

The U.S. long has been frustrated by Islamabad's refusal to target Afghan Taliban militants and their allies using Pakistani territory to stage attacks against U.S. and coalition troops in Afghanistan. Many analysts believe Pakistan is reluctant to target the groups because they have strong historical ties with them and could use them as allies after foreign forces leave Afghanistan.

Panetta spoke optimistically about U.S. relations with Pakistan's military, saying they have improved "a great deal" lately, after a falling out over American airstrikes that killed 24 Pakistani soldiers in November. Pakistan subsequently closed border crossings to U.S. and coalition military shipments, but recently re-opened them.

He said Allen and Kayani have "discussed concerns" about the Haqqanis, whose fighters move back and forth across the border to launch attacks in Afghanistan.

"Gen. Kayani did indicate that they had developed plans to go into Waziristan," Panetta said. "Our understanding is that hopefully they're going to take that step in the near future. I can't tell you when. But the indication that we have is that they are prepared to conduct that operation soon."

Pakistan has denied this, saying its forces are stretched too thin fighting Pakistani Taliban militants at war with the state. It also has criticized NATO and Afghan forces for not doing enough to stop Pakistani militants holed up in Afghanistan from launching attacks across the border into Pakistan.

Touching on another major U.S. frustration in Afghanistan, Panetta said the accelerating pattern of attacks on American and coalition troops by Afghan army and police members is a sign that the Taliban is grasping for success. But he added that U.S. military commanders say such attacks still remain "sporadic" and not a long-term trend.

He argued that the Afghan insider attacks, in which numerous Afghan troops have turned their guns on coalition forces, may reflect efforts by the Taliban to use unconventional tactics against a coalition force that it cannot defeat on the battlefield.

In other comments, Panetta said the U.S. is providing additional military assistance to peacekeeping forces in Egypt's Sinai Peninsula in order to strengthen security in the region. But he said that so far the Pentagon has not moved to send additional U.S. troops to the Sinai. A truck-mounted tracking system sent to the Sinai will allow troops to follow friendly forces.

"We just want to make sure that we know how those forces are deployed in order to ensure that we can more effectively go after those terrorists that would try to create an incident or terrorist act," Panetta said.

Currently the U.S. has about 800 troops in the Sinai as part of an international peacekeeping force. Panetta did not rule out sending more U.S. forces to the Sinai, but said America is working closely with Egyptian leaders "to determine what additional help they may need in order to ensure that that area is secured."

Just over a week ago, masked militants killed 16 Egyptian soldiers at a checkpoint along the border with Gaza and Israel, then burst through a security fence into Israel. Israel detected the infiltration and launched an airstrike to stop the assault.

___

Associated Press National Security Editor Wendy Benjaminson contributed to this report.

___

Follow Lolita C. Baldor at http://twitter.com/lbaldor and Robert Burns at http://twitter.com/robertburnsAP