NEW YORK, Sept. 9 (UPI) -- Insurgent attacks on candidates and Afghanistan's inability to guarantee safety for voters will damage an upcoming election, a watchdog group says.

The Taliban have claimed responsibility for killing three political candidates since July, and Afghanistan's Sept. 18 parliamentary election will suffer as a result, Human Rights Watch said in a statement Thursday.

"Taliban attacks and the broad lack of confidence in the Afghan government to conduct a secure election threatens its validity," Rachel Reid, Afghanistan researcher at Human Rights Watch, said in the statement. "Insurgent violence, particularly against women candidates, was inevitable, but the government's weak response was not."

The organization said candidates and election officials who feared violence and corruption in the upcoming election contacted the human rights group.

This is the second parliamentary election since the fall of the Taliban; the first was in 2005. The 2009 presidential and provincial elections were marred by violence, poor security and allegations of corruption, Human Rights Watch said.