Afghanistan's security forces take over from Nato Afghan policemen ride on a vehicle as they leave the site of a blast in Kabul which coincided with the security handover from Nato troops in another part of the city. Photograph: Massoud Hossaini/AFP/Getty Images The Afghan president, Hamid Karzai, has announced at a ceremony that his country's armed forces are taking over the lead for security nationwide from the US-led Nato coalition. The handover of responsibility is a significant milestone in the nearly 12-year war and marks a turning point for American and Nato forces, which will now move entirely into a supporting role. It also opens the way for their full withdrawal in 18 months. "This is a historic moment for our country and from tomorrow all of the security operations will be in the hands of the Afghan security forces," Karzai said at the ceremony on Tuesday, held at the new National Defence University built to train Afghanistan's military officers. Karzai said that in the coming months, coalition forces will gradually withdraw from Afghanistan's provinces as the country's security forces replace them. In announcing the fifth and final phase of a process that began at a November 2010 Nato summit in Lisbon, Portugal, Karzai said "transition will be completed and Afghan security forces will lead and conduct all operations." Nato secretary-general Anders Fogh Rasmussen said it would provide military help if and when needed but will no longer plan, execute or lead operations. Alliance training since 2009 has dramatically increased the size of the Afghan national security forces, bringing them up from 40,000 men and women six years ago to about 352,000 today. After transition, coalition troops will move entirely into a supporting role - training and mentoring, and in emergency situations providing the backup to the Afghans in combat, mainly in the form of airstrikes and medical evacuation. Ten years ago, there were no Afghan national security forces. Five years ago, Afghan forces were a fraction of what they are today. Now you have 350,000 Afghan troops and police. A formidable force. And time and again, we have seen them dealing quickly and competently with complex attacks. Defeating the enemies of Afghanistan, and defending and protecting the Afghan people," Rasmussen said. Afghans will now have the lead for security in all 403 districts of Afghanistan's 34 provinces. Until now, they were responsible for 312 districts nationwide - about 80% of Afghanistan's population of nearly 30 million. The handover paves the way for coalition forces - currently about 100,000 troops from 48 countries, including 66,000 Americans - to leave. By the end of the year, the Nato force will be halved. At the end of 2014, all combat troops will have left and will be replaced, if approved by the Afghan government, by a much smaller force that will only train and advise. Barack Obama has not yet said how many US soldiers he will leave in Afghanistan along with Nato forces, but it is thought that it would be about 9,000 US troops and about 6,000 from its allies. The US and its allies have already pledged to fund the Afghan forces in the immediate years after 2015. The handover was marred by a botched bomb attack against an Afghan politician in another part of Kabul. The bombing killed three civilians. Kabul deputy police chief Mohammad Daoud Amin said the blast was in the Pul-e-Surkh area in the west of the city, several miles from the site of the handover ceremony. A police officer named Asadullah said the target was the convoy of Mohammed Mohaqiq, a prominent ethnic Hazara lawmaker who is a former cabinet member. Asadullah, who like many Afghans uses just one name, said he saw two dead bodies lying in the street and a police vehicle was destroyed in the blast. Mohaqiq survived the blast, according to Nahim Lalai Hamidzai, another member of the Afghan parliament. General Mohammad Zahir, chief of the Kabul criminal investigation division, said three people were killed by the bombing and another 30 were wounded - including six bodyguards. The roadside bomb targeted the Mohaqiq convoy, but he safely passed. One of his vehicles was damaged," Zahir said. Mohaqiq, the leader of the People's Islamic Unity party of Afghanistan, is a member of the National Front, which represents members of the former Northern Alliance who fought the Taliban before the US invasion in 2001. The predominantly ethnic Pashtun Taliban persecuted the Hazara minority during their five-year rule that imposed a radical interpretation of Islamic law. The Taliban insurgency has been carrying out an intense campaign of violence in the runup to Tuesday's security handover.