BRUSSELS (Agencies) - European Union leaders on Friday agreed to examine all necessary options to protect civilians in Libya as they ramped up pressure on Moamer Gaddafi at a crisis summit. Opening a door to possible military intervention, the 27-nation bloc agreed a statement expressing its deep concern about attacks against civilians, including from the air. In order to protect the civilian population, member states will examine all necessary options, provided that there is a demonstrable need, a clear legal basis and support from the region, the statement said. The legal basis sought by EU states would be a United Nations Security Council resolution authorising action. European nations have also repeatedly insisted they would take action in Libya only with approval from the Arab League, which will discuss events in Libya in Cairo on Sunday. Fridays pivotal summit capped 48 hours of talks in response to the crisis in Libya, also involving NATO defence ministers and European Union foreign ministers. The EU also deemed the opposition to Gaddafi, based in the eastern city of Benghazi, a legitimate interlocutor. France has officially recognised the opposition as the rightful representative of Libya but other EU states have stopped short even as they insist that Gaddafi immediately step down. Gaddafi must give up power without delay, said EU president Herman Van Rompuy at the close of the summit on the conflict in the north African nation. Gaddafi was a leader shooting at his own people, Van Rompuy said. The Libyan leadership must give up power without delay, he added. All say it loud and clear, Van Rompuy said of the EU leaders. In other developments at the talks, British Prime Minister David Cameron called on the European Union and international community to consider imposing additional sanctions on Libyas oil industry. Camerons call came as multi-billion-dollar EU sanctions on Libya came into force on five state vehicles holding billions in assets and investments said to be under Gaddafis family control. The EU Official Journal named the Libyan Investment Authority - also known as the Libyan Arab Foreign Investment Company - among the five, as the overseas vehicle for investing Tripolis oil revenues and under control of Moamer Gaddafi and his family, and a potential source of funding for his regime. Meanwhile, Libyan rebels battled troops loyal to Moamer Gaddafi outside Ras Lanuf on Friday, finding themselves on the back foot and outgunned a day after the regime recaptured the key oil town. As the two sides exchanged rocket and shell fire east of town, fighter jets screeched over rebel positions on bombing runs, hitting a building used as a checkpoint and setting ablaze an oil storage tank at a nearby refinery. Another strike hit rebel positions 15 kilometres (nine miles) east of town, the juddering blast sending a huge plume of sand and smoke into the sky.