But he noted that he could not speak on behalf of his Lib Dem colleagues in government. “Obviously I can’t apply my pledge to the Lib Dems and obviously they need to improve their diversity and I’ll be having a word with the deputy prime minister about that," he said.
"I remain committed to what I said. I want to deliver a more diverse party and I want to encourage more women and more ethnic minorities, more people from different parts of the country, from different backgrounds, into the party at all levels," he said.
The Lib Dems currently have five cabinet ministers in the government - all of them are men. Of the junior Lib Dem ministers, six are women, including Lynne Featherstone at international development and Jo Swinson at the business department.
Cameron has frequently been criticised for not appointing enough women to top government jobs. Of only four full cabinet members are women, Justine Greening (transport), Maria Miller (culture), Theresa Villers (Northern Ireland) and Theresa May (Home Office).
The prime minister said the reason many junior ministers lost their jobs in September's reshuffle was so he could bring in new MPs, especially female and ethnic minority Tories, with a view to promoting them in the future.
“You can’t just catapult people into the Cabinet. You need to give people the chance to shine in junior ministerial jobs so that’s what I’ve done, " he said.
"These reshuffles are important because you can’t just fix it in one go. You need to get the talent moving through the ranks."
Cameron also said there was a "never ending drive" to see more MPs from ethnic minorities elected to parliament.
He told House magazine: "The Conservative Party needed to reach out as I’ve put it in the past people were opening a door hand seeing all white faces and didn’t find that very welcoming, we need to go out and attract very talented people from ethnic minority communities to join the Conservatives, stands as a Conservatives, stand for local government, stand for Parliament, so there’s no let up in that, we’ll go on encouraging that."