US labels Syrian rebel group "terrorists" The US has designated the extremist Syrian rebel group Jabhat al Nasra a terrorist organisation ahead of a key diplomatic meeting on Syria in Marrakesh on Wednesday. Jabhat al Nasra was entered into the Federal Register on Monday as an alias of al-Qaeda in Iraq. The move, which was trailed last week, makes it illegal for Americans to do business with the group. Though it appears intended to marginalise jihadi elements in the rebellion, the designation has the potential to complicate the US's relationship with other forces fighting Syrian president Bashar al Assad. Last week, Syrian rebel groups announced the formation of a new unified military command at a meeting in Turkey attended by security officials from western powers. The rebels are hoping greater international engagement with the newly organised opposition, which Wednesday's Friends of Syria Meeting of regional and international powers in Morocco is supposed to facilitate, will result in a fresh supply of weapons. Jabhat al Nasra was excluded from the meeting in Turkey but is deeply involved in the rebellion on the ground, and has played a prominent role in recent gains, including Sunday's storming of part of a key military base near Aleppo. Little is known about the group, which first emerged when it claimed responsibility for suicide bomb attacks in Damascus and Aleppo at the beginning of this year. It has received the endorsement of online jihadi forums, and is said to have a stock of experienced foreign fighters. Though many in the Syrian opposition disagree with Jabhat al Nasra's ideology, its members are respected for their bravery and competence in battle, and the US move has already provoked a backlash in some parts of Syria. The escalating scale of Syria's civil war was underscored on Tuesday when the UN refugee agency announced that the number of refugees it had sent fleeing into neighbouring countries had topped half a million. "According to UNHCR's latest figures for Lebanon, Jordan, Iraq, Turkey and North Africa, 509,559 Syrians are either already registered (425,160) or in the process of being registered," UNHCR said in a statement issued in Geneva. The number of registered Syrian refugees region-wide rose by about 3,200 per day in November, and close to 1,000 Syrians crossed into Jordan during the past two nights alone, it said. Lebanon is now host to 154,387 registered Syrian refugees who have fled the 20-month-old conflict, Jordan has 142,664, Turkey 136,319, Iraq 65,449 and North Africa 11,740, the UN High Commissioner for Refugees (UNHCR) said. In addition, large numbers of Syrians have crossed into neighbouring countries but have not yet come forward to register for refugee status and assistance, it said. They include about 100,000 in Jordan, 70,000 each in both Turkey and Egypt and tens of thousands in Lebanon, it said, citing government estimates.