"The German armed force and foreign intelligence service BND have violated the constitution and laws by assisting in the NATO killing lists," Left Party lawmaker Jan van Aken told Bild newspaper Tuesday.
German weekly Der Spiegel published secret NATO documents revealing a list of around 750 suspected Taliban officials, some of whom were killed without charge or trial.
The list was prepared between 2009 and 2011 and was based on intelligence gathered by secret services of several allies, according to the weekly.
The German government had long insisted that it did not take part in any targeted killings in Afghanistan where it deployed around 5,000 soldiers since 2002 as part of NATO's mission.
On Tuesday, Bild newspaper published a secret document suggesting German secret services passed on intelligence about suspected Taliban leader Qari Yusuf to NATO units, information believed to have been used in an operation to kill him.
The secret document involved Yusuf's cell phone number, which was used to identify his location.
Hans-Christian Stroebele, a senior lawmaker and member of the opposition Green Party, harshly criticized the government and said that the parliament was not informed about these practices.
"The government must now clear the air and immediately clarify who was responsible for misinforming the parliament on this issue and for contributing to these targeted killings," Stroebele told German media.
The German army said in a statement on its web page that the NATO lists that involve suspected Taliban leaders and officials do exist, but denied that it was a killing list. The armed forces said the goal was to arrest those suspects.
Human right organizations have long criticized targeted killings in Afghanistan, which killed hundreds of suspected Taliban members without trial. According Der Spiegel, not only Taliban commanders were targeted, but also suspected drug dealers.
Many of these operations involved drones or helicopters and resulted in hundreds of civilian deaths, according to the weekly. In 2009 alone, around 600 civilians were killed in these operations.
Germany’s military role in Afghanistan has been a sensitive issue in domestic politics as a majority of Germans have been reluctant to see their country involved militarily in international conflicts.
German government officials, however, have advocated a more active foreign policy approach, supported by military measures, citing Germany's responsibility for "international peace and stability."
Germany had been one of the key contributors to the NATO-led International Security Assistance Force mission in Afghanistan since 2002 and has provided up to 5,350 soldiers, in the country's first international combat operation carried out by its modern, post-WWII army.
Fifty-five German soldiers have lost their lives in Afghanistan, 35 of them in attacks or during military operations.
The German government has decided last month to keep 850 soldiers in Afghanistan after the withdrawal of NATO’s combat troops at the end of 2014.
From Jan. 1, 2015, the NATO-led mission will focus on training and advising Afghan security forces. The 13,000 foreign troops for the Resolute Support Mission will come from 28 NATO allies and 14 other partner nations.