Kandahar - A Taliban suicide bomber killed at least 13 people and wounded several more in an attack on a convoy of Afghan soldiers in Helmand province late on Sunday, an official said.It was the latest in a series of deadly blows to Afghanistan's beleaguered security forces and yet again underlined spiralling insecurity in the war-torn nation."A suicide bomber detonated an explosive-filled car as the Afghan National Army convoy passed a small market in Nawa District of Helmand," Omar Zwak, a spokesman for the provincial governor, told AFP.He added that civilians and forces personnel were among the dead while more than a dozen others had been wounded.A source working at a nearby hospital told AFP on condition of anonymity that the bodies of 15 victims had been brought to the hospital. Another 19 injured were also admitted, he added."The majority of the dead belong to Afghan forces and most of the wounded are civilians," the source said.Fighting seasonThe Taliban claimed responsibility for the attack in a WhatsApp message sent to journalists.The deadly assault came days after a Taliban suicide bomber killed five civilians and wounded dozens of others, mainly children, when he detonated a car filled with explosives at a police headquarters in Lashkar Gah, Helmand's capital.That attack was the insurgents' first major one since US President Donald Trump announced he was committing American troops to Afghanistan indefinitely.The resurgent Taliban are at the peak of their summer fighting season and have been ramping up their campaign against government forces.Afghan police and troops - beset by a high death toll, desertions and non-existent "ghost soldiers" on the payroll - have been struggling to beat back the insurgents since US-led NATO troops ended their combat mission in December 2014.Casualties among Afghan security forces soared by 35% in 2016, with 6 800 soldiers and police killed, according to US watchdog SIGAR.More than 2 500 Afghan police and troops were killed from January 1 to May 8.Ordinary Afghans have also paid a heavy price for the 16-year US-led war.Civilian deaths are at their worst since records began in 2009. In the first half of the year, 1 662 civilians were killed and more than 3 500 injured, according to the United Nations.Analysts have warned that Trump's commitment to sending thousands more American troops to Afghanistan - reversing earlier pledges to pull out - could fuel the insurgency and lead to more casualties.The Taliban had called for a complete withdrawal of foreign forces and, following Trump's announcement, vowed to make the country a "graveyard" for US forces.