Volkswagen's US boss has offered a "sincere apology" for the emissions scandal and vowed "this will never happen again".
Michael Horn was giving evidence before a US House of Representatives sub-committee in which he admitted that VW had lost trust from its customers, the car industry and regulators but was "determined to make things right".
He told the Washington-based hearing: "On behalf of our company, my colleagues in Germany and me personally, I would like to offer a sincere apology for Volkswagen's use of a software programme that served to defeat the regular emissions testing regime."
The German car giant has admitted that four-cylinder diesel cars produced from 2009 to 2015 had software that helped them cheat emissions tests. The admission came after the company was confronted by the US Environmental Protection Agency and California regulators, sparking a worldwide scandal which involves 11 million vehicles.
Close to 1.2 million vehicles are affected in the UK.
Mr Horn said: "These events, and I fully agree on this, are deeply troubling. I did not think that something like this was possible at the Volkswagen group. We have broken the trust of our customers, leaderships, employees as well as the public and the regulators.
"Let me be very clear - we at Volkswagen take full responsibility for our actions and are working with all the relevant authorities in a co-operative way."
A recall is expected to start in the new year, with the aim of having all affected cars fixed by the end of 2016.
Volkswagen is to halt delivery of its 2016 Jetta, Golf, Passat and Beetle diesel models in the US - raising speculation that the emissions-cheating device similar to those in earlier models is also in its new vehicles.
Investigations have been launched worldwide to find out what happened in order to hold those involved responsible.
Mr Horn, who insisted the vehicles are safe to drive, said compliance processes and standards within VW will be examined so this cannot happen again.
He also said there would be open communication with customers in the future "in the hope of making things right" but was aware that actions would be more powerful than words in turning around this damaging situation.
Transport Secretary Patrick McLoughlin has stressed the importance of protecting UK consumer interests in the wake of the admission by VW on its use of defeat devices.
Mr McLoughlin, who was meeting of European transport ministers in Luxembourg, also urged the European Commission to introduce real-world driving emissions tests as soon as possible.
He said the UK has started its own testing programme which will seek "to get to the bottom" of what the situation is for VW Group cars in the UK. The UK will re-test Euro 5 category diesel cars which VW group has confirmed contain the defeat device software.
This will involve both laboratory and real-world tests. .
Mr McLoughlin said: "The needs of consumers must be at the forefront of action to restore public confidence in emissions testing. I have made it clear to Volkswagen that we expect it to support UK owners of vehicles fitted with defeat device software.
"The UK Government has already announced that owners in Britain will not incur higher vehicle taxes as result of VW's actions.
"There now needs to be co-ordinated European work to establish trust in the testing process. As I highlighted to the Transport Council, driving emissions tests that reflect real-world performance must be introduced as quickly as possible."