Volkswagen has suspended its top lobbyist following revelations that it funded tests that exposed monkeys to diesel fumes.

The German carmaker said Tuesday that Thomas Steg, its head of external relations and sustainability, will remain suspended until the issue has been fully investigated.

"We are currently in the process of investigating the work ... and drawing all the necessary consequences. Mr. Steg has declared that he will assume full responsibility," Matthias Mueller, CEO of Volkswagen Group, said in a statement.

Volkswagen (VLKAY) acknowledged Monday that it helped finance a 2014 study in which caged monkeys were forced to inhale fumes from a diesel Beetle.

The New York Times first reported on the study last week. The tests are also mentioned in the premier episode of the Netflix documentary series "Dirty Money."

The study was part of an attempt to prove that new diesel engines were cleaner than their predecessors. The test vehicle was rigged to reduce emissions, part of a much bigger scandal that would later cost Volkswagen tens of billions.

The monkeys used in the study were exposed to fumes for several hours, before being subjected to medical tests.

The research was commissioned by the European Research Group on Environment and Health in the Transport Sector (EUGT), an institute established by Volkswagen (VLKAF), Daimler (DDAIF), BMW (BMWYY) and parts supplier Bosch.

Tests were conducted by the Lovelace Respiratory Research Institute, which is based in New Mexico. Volkswagen said the project was "not completed or published" before the EUGT was dissolved in June 2017.

Related: Monkeys were used to test diesel fumes, German carmakers say

Fallout has been swift.

The German government joined animal rights groups in condemning the tests on Monday.

'These tests ... are in no ethical way justifiable and they raise many critical questions about those who are behind the tests," said Steffen Seibert, a spokesman for German Chancellor Angela Merkel.

Hans Dieter Pötsch, chairman of Volkswagen's supervisory board, said Monday that he would "do everything possible to ensure that this matter is investigated in detail."

"Whoever is responsible for this must of course be held accountable," he added.

Daimler said it was "appalled by the nature and extent of the studies and their implementation." BMW has not responded to multiple requests for comment.

Steg has been working for Volkswagen since 2012. He previously served as deputy spokesperson for the German government under Chancellor Gerhard Schroeder.