Media playback is unsupported on your device Media caption Kirsty Williams kept her seat but the four other Lib Dem AMs lost

Kirsty Williams is stepping down as leader of the Welsh Liberal Democrats.

She increased her majority in Brecon and Radnorshire at the assembly election, but is now the only Lib Dem AM left after the other four lost.

Ms Williams said she had to "take responsibility" for the result, but said she would have stepped down anyway after eight years as leader.

Ceredigion MP Mark Williams will serve as acting leader, pending a decision on how to run any leadership contest.

"It's the right time for the party to have somebody new to pick up the challenge, bringing up new ideas and to drive the party forward," Ms Williams told BBC Wales.

"I also have to take responsibility for the result that we have had. So it seems only right that I make this decision, and make this decision now."

UK Liberal Democrat leader Tim Farron said he was "sorry" she had stood down and added he was "certain that Kirsty will play a key role in the future of our party".

A member of the Welsh Assembly since its creation in 1999, Ms Williams was elected Welsh Lib Dem leader in December 2008.

The Lib Dems finished fifth in the constituency vote on Thursday evening with 7.7%, down 2.9% on 2011 when they won five seats.

Their tally of one AM is their worst ever.

The Lib Dems have won five or six seats at every previous election, and had ministers in a coalition government with Labour from 2000 to 2003.