British Prime Minister David Cameron was forced Monday to scrap a visit to an Afghan town he had held up as an example of improved security after a soldier went missing in the area. International forces have launched a huge manhunt for the British soldier, who disappeared just hours before Cameron began a surprise visit to southern Helmand province to announce Britain would withdraw more of its 9,500 troops. Cameron said he had cancelled a planned trip to the town of Lashkar Gah, where Britain is handing over control of security to Afghan forces, so British helicopters and ground forces could continue their hunt. \"I arrived here today and received the news about this very worrying incident of a British soldier going missing in central Helmand,\" he told reporters after he arrived on a Royal Air Force plane at the Camp Bastion base. \"I was just very clear that you\'ve got something like that absolutely urgent taking place, where you want to concentrate all the assets and ability that you have to try and find this person and bring it to the right conclusion. \"Its just absolute common sense that the military should concentrate on the most important requirement of all which is to help and find this person rather than to bother flying me around.\" Afghan police in the southern province of Helmand, where mostly American and British troops are fighting the Taliban insurgency, said the man had been kidnapped in the Gereshk area of Nahri Sarraj district. The Taliban claimed that its fighters had kidnapped and killed a British soldier in Helmand, but there was no independent confirmation and the militia is known to routinely exaggerate its claims. Lashkar Gah was one of seven initial handover areas in Afghanistan identified by foreign forces ahead of a full transfer of responsibility across the country and the withdrawal of all western combat troops by the end of 2014. After years of Taliban violence Lashkar Gah was seen as the most unlikely candidate among those chosen for early transition. But Cameron said the campaign against Taliban militants had entered a \"new phase\" ahead of the deadline and that Afghanistan\'s army and police were \"increasingly confident\". \"As that happens, there will be opportunities to bring British soldiers home, but we are talking relatively small numbers and over a period of time,\" Cameron said. Cameron said he would make a full announcement in the British parliament on Wednesday. Reports at the weekend said he would order the withdrawal of 500-800 troops by the end of 2012. He said Monday that \"you\'re not going to see a radical change (in numbers) before the next fighting season\" next year. The British premier said Afghan security forces were carrying out more operations on their own and that there was now a \"proper transition taking place, including the town of Lashkar Gah itself\". The British contingent is the second-largest in Afghanistan after the United States. Cameron\'s announcement comes nearly two weeks after US President Barack Obama announced that he would withdraw 33,000 US \"surge\" troops from Afghanistan by the end of 2012, bringing total US forces there down to 100,000. The speed of that drawdown has been slammed by senior Republican lawmakers in the United States, and met with a cool reception by US military commanders. Britain\'s Ministry of Defence confirmed that a British serviceman had gone missing in central Helmand in the early hours of Monday, without giving any further details of what had happened. \"An extensive operation to find him is underway,\" it said in a statement. The NATO-led International Security Assistance Force (ISAF) also said \"an active search effort\" was underway to find the soldier. Defence Secretary Liam Fox confirmed the disappearance during questions in the House of Commons and said the soldier\'s family were being kept informed. Last week marked the second anniversary of the kidnapping of a US soldier, Bowe Bergdahl, who was captured by Taliban believed to be allied to the militant Haqqani network from his base in Paktika near the Pakistan border.