TRIPOLI/KIKLA, Libya - NATO warplanes attacked Tripoli on Tuesday night after Libyan rebels pushed back forces loyal to leader Muammar Gaddafi on three fronts, bringing them closer to the capital.The strikes followed a lull in NATO bombing of Tripoli on Tuesday, but in the evening loud blasts rocked the city with plumes of smoke filling the sky to the east and aircraft flying overhead.Libyan state TV said the bombs had struck military and civilian targets in Firnag, one of the most populated areas in the capital, and Ain Zara. It said there were casualties.Earlier in the day rebels tried to advance in the east, setting their sights on the oil town of Brega to extend their control over the region, epicenter of the four-month rebellion against Gaddafi's four-decade rule.NATO defense chiefs met in Belgrade to discuss the mission, after U.S. Defense Secretary Robert Gates accused some European allies of failing to pull their weight.A senior NATO commander appeared to raise questions about the alliance's ability to handle a long-term intervention in Libya."We are conducting this operation with all the means we have, and the best we can. If the operation were to last long, of course, the resource issue will become critical," General Stephane Abrial said.In a sign that Gaddafi forces may be getting stretched, the rebels seized the town of Kikla, 150 km (90 miles) southwest of Tripoli. They also pushed several kilometres west of their Misrata stronghold to the outskirts of government-held Zlitan.Nato leaflet warningThe push to Kikla followed weeks of deadlock between the rag-tag rebel army and government forces, though air strikes by NATO have taken their toll on Gaddafi's better-equipped troops.A NATO leaflet drop warning of helicopter strikes prompted some rebels to retreat from their newly captured positions outside Zlitan."We came back because of the leaflets from NATO. I hope there is some coordination between the fighters and NATO ... Is it logical that NATO has no idea we took those positions?" said local commander Mohammed Genei.A NATO official said the alliance did drop leaflets warning of the possibility of attack by helicopters, but said this was west of Misrata, and closer to Zlitan.Even without the threat of NATO attack, the rebels said they would not attack Zlitan, citing tribal sensitivities. Instead they would wait for the local inhabitants to rise up.A NATO official said warplanes had hit an ammunition store at Waddan, not far from Al Jufrah, after Libyan television said Al Jufrah, in central Libya, had been bombed for a second day.Tunisia flew an F-5 warplane and a helicopter along its border with Libya after Libyan troops fired several rockets into Tunisia.The explosions, close to rebel territory in Libya's Western Mountains southwest of Tripoli, caused no damage or injuries.A Reuters journalist in Ryayna, 15 km east of Zintan in the Western Mountains, said rebels had taken the village and pushed back Gaddafi's forces.The rebels, who had been trying to seize Ryayna for several weeks, said two of their fighters had been killed, but they had taken prisoners, including foreign fighters."We have captured 15 pro-Gaddafi soldiers, three of them were Libyans and the remaining 12 were either Chadians or Touaregs," rebel spokesman Abdulrahman said from Zintan.