As a part of its proposal to provide military aid to the Syrian rebels, the United States is studying setting up a limited no-fly zone in Syria close to the southern border with Jordan in order to protect Syrian refugees and rebel forces training in the area, two senior Western diplomats in Turkey said on Friday.Their comments, confirmed by a third regional diplomat, came after Washington said it would step up military assistance to rebels battling President Bashar Assad in response to what it said was proof of chemical weapons use by Assad's forces. "Washington is considering a no-fly zone to help Assad's opponents," one diplomat said. He said it would be limited "time-wise and area-wise, possibly near the Jordanian border," without giving details.The Wall Street Journal reported that the no-fly zone would stretch up to 25 miles into Syria, and would be enforced with aircraft flown from Jordan or from Navy ships in the Mediterranean or Red Sea.US officials told the Journal the White House is considering proposals to arm and train the rebels in Jordan, but that Washington could decide to train rebels in Jordan without enforcing the no-fly zone.The limited no-fly zone would cost an estimated $50 million a day, and would take a month to get up and running. However, the window of opportunity to set it up is limited. If Russia decides to deliver the S-300 anti-aircraft missiles to the Assad regime, it would become too dangerous for US pilots to enforce the buffer zone, the officials told the Journal.Imposing a no-fly zone would therefore require the United States to destroy Syria's air defenses, entering the two-year-old civil war with the sort of action that NATO used to help topple Muammar Gaddafi in Libya two years ago.Despite that, the officials said the no-fly zone would not necessitate the destruction of Syrian anti-aircraft batteries.The area near the Jordanian border contains some of the most densely-populated parts of Syria, including the outskirts of the capital Damascus.Washington has moved Patriot surface-to-air missiles, war planes and more than 4,000 troops into Jordan in the past week, officially as part of an annual exercise, but making clear that the forces deployed could stay on when the war games are over.A White House National Security Council spokeswoman declined to comment on the topic.France: UN backing for Syria no-fly zone 'unlikely'France said on Friday that it was unlikely for now that a no-fly zone would be established over Syria because of opposition from some members of the UN Security Council."The problem with this type of measure is that it can only be put in place with approval from the international community," French Foreign Ministry spokesman Philippe Lalliot told journalists."A decision from the United Nations Security Council is needed, and not just any decision," he said. A Chapter 7 resolution authorizing military action was needed, and that was unlikely to be passed, he added.Assad's government can count on Moscow to block any such resolution if it were to be brought to a vote.Lalliot said France had yet to make a decision on arming rebels, but that all these issues would be discussed among heads of state at next week's G8 summit.Apart from arming the rebels, France could also extend further help to them in the form of sharing more intelligence, providing training and planning operations, Lalliot added.He declined to say whether that meant French military advisers would be on the ground in Syria, although diplomatic sources have indicated some are already operating in Turkey and Jordan.Rebels demand advanced weaponsThe White House said Washington would now provide "direct military support" to the opposition. It did not publicly specify whether this would include "lethal aid," which would mark a reversal of Obama's previous resistance to arming the rebels. But a US official, speaking on condition of anonymity, said the package would include weapons.Syrian rebels already receive light arms from Saudi Arabia and Qatar. They have asked for heavier weapons including anti-tank and anti-aircraft missiles. European countries, in particular France, have argued that the solution is to provide more weapons for mainstream rebels to marginalize extremists."We want anti-tank and anti-aircraft weapons," George Sabra, acting leader of the National Coalition political opposition bloc, told Al Arabiya television. "We expect to see positive results and genuine military support."Syrian rebel commanders were due to meet Western and Turkish officials in Turkey on Friday to discuss military assistance to the rebels. Until now Washington has been deeply reluctant to send weapons, citing a risk that they would end up in the hands of radical Sunni Muslim brigades.One of the diplomats said that setting up a no-fly zone could also help Western efforts to monitor the recipients of any arms supplies.Free Syria Army General Salim Idris told Al Arabiya that the Syrian opposition hopes to translate the change in American position into reality, and be given tangible access to weapons and ammunition. He also warned that if the US backtracks on its decision to arm the rebels, Iran and Hezbollah would cement their control over the region.US Senator John McCain, a hawk on Syria, said America needed to neutralize Assad's air power: "They (rebels) have enough light weapons. They've got enough AK-47s. AK-47s don't do very well against tanks," McCain told CNN. "They need anti-tank weapons and they need anti-air weapons."NATO Secretary-General Anders Fogh Rasmussen welcomed what he said was a "clear US statement". "The international community has made clear that any use of chemical weapons is completely unacceptable and a clear breach of international law," Rasmussen told reporters in Brussels.