A Taliban suicide car bomber struck a NATO convoy in the Afghan capital Tuesday, killing six troops, five of them American, officials said. Twelve Afghan civilians also died – many of them on a public bus in rush-hour traffic. The powerful blast occurred on a major Kabul thoroughfare that runs by the ruins of a one-time royal palace and government ministries. It wrecked nearly 20 vehicles, including five SUVs in the NATO convoy, and scattered debris and body parts across the wide boulevard. The body of woman in a burqa was smashed against the window of the bus. The attack – the deadliest for NATO troops in the capital since September – comes despite a ramped up effort by Afghan authorities to intercept would-be attackers and better secure a capital city that saw a spate of brazen attacks this winter. In the last such attack in February, suicide bombers stormed two small downtown hotels and killed 16 people.