Six civilians were killed Wednesday by a roadside bomb that bore the hallmarks of Taliban militants, while American forces killed four people in southern Afghanistan who residents said were also civilians. The violence is unfolding less than three weeks before the country's presidential election, with many polling stations in areas where control is under dispute. Afghan forces and those of the American-led coalition are trying to secure the country to make voting safe during the election, scheduled for Aug. 20. Taliban militants are urging Afghans to boycott the voting. The civilians, as ever in war, are being caught in the middle. In the first attack, a roadside bomb killed two tribal elders and their four bodyguards Wednesday morning in the Pachir Agam district of Nangahar province in eastern Afghanistan. The elders were on their way to a meeting to discuss road security. All six of the men were killed instantly. A spokesman for the Taliban, going by the name of Zabiullah Mujahid, denied the group's involvement in the attack. But roadside bombs are increasingly the group's weapon of choice to kill American and Afghan soldiers. Nearly as often, the bombs kill civilians as well. In the second episode, American officials said a helicopter killed four armed men Wednesday morning as they traveled on motorcycles through an open area in the Argundab district of Kandahar province. The men were carrying plastic jugs in an area where roadside bombs are common, suggesting that they were carrying explosive materials, according to a communiqu? released by the American-led force here. The Americans said that the men were killed by bullets and rockets and that no bombs were dropped. But civilians in the area told a very different story. They said the four victims were all civilians: Hajji Rahim, a local tribal leader, and his three sons. According to witnesses, the four were killed in their home in the village of Kohak in the Argundab district. After the airstrike, angry villagers carried the bodies to a guest house owned by Kandahar's governor and chanted anti-American slogans. 'These are the enemies of Muslims!' the crowd roared. A correspondent for the Reuters news agency who saw the bodies said two of them appeared to be teenage boys. 'They were civilians killed by the airstrike, while fast asleep,' Jan Mohammed, one of the men who carried the bodies, told Reuters. Afghan and American authorities said they were looking into the accusations. Civilian deaths have been a source of extreme animosity between the American-led coalition and their Afghan hosts, particularly those caused by airstrikes. Gen. Stanley A. McChrystal, the overall commander here, recently tightened the rules covering airstrikes in order to lower the number of civilian deaths. As the Afghan war has intensified in recent months, more civilians have died. A U.N. report released last week said that 1,013 civilians were killed in the first six months of 2009, compared with 818 in the same period last year. Insurgents were to blame for 59 percent of those deaths, the report said. 