Facebook's chief technical officer, Mike Schroepfer, has told the Department for Digital, Culture, Media & Sport (DCMS) select committee that he is "disappointed" by the social media giant's handling of Russian disinformation campaigns on the platform.
Facing a grilling by committee chair Damian Collins about political advertising, Mr Schroepfer said: "We were slow to understand the impact at the time and I am way more disappointed in this than you are."
Amid laughter, Mr Collins told Mr Schroepfer: "It's a high bar."
The Facebook executive replied: "I'm sorry, I shouldn't have said that. It's something we're working very hard on."
Mr Schroepfer is answering questions about how malicious actors used Facebook to impersonate people and attempt to influence elections with political advertising.
Mr Schroepfer stressed that political advertising on Facebook is "a very small, low, single-digit percentage of our advertising revenue" and the company believes transparency is the best way to protect voters from malicious political ads.
"There are a number of challenges you've raised and we need to do better," he said, but added that, for people outside the political mainstream, the combination of Facebook pages and advertising on the platform is "a powerful tool of free speech".
The solution, he claimed, is greater transparency around who is paying for political adverts on Facebook and making the content of those adverts visible to everyone.
In written evidence provided before the hearing, Mr Schroepfer detailed plans to create a "searchable archive" of political adverts in time for the UK local elections in May 2019.