Ieuan Wyn Jones led Plaid Cymru for less than three years
Ieuan Wyn Jones is to resign as leader of Plaid Cymru after his party's poor performance in the Welsh assembly election.
The dramatic announcement shocked his party, a week after Plaid suffered major losses in the poll.
Mr Jones made his decision after half the 12 Plaid assembly members said they wanted him to go immediately.
It provoked angry recrimination in the party, and one Plaid MP said he was disgusted the AMs moved so quickly, and failed to consult anyone outside the assembly.
Mr Jones, 53, had said in the wake of last week's election that he was determined to stay on, even though he admitted the election result was "deeply disappointing".
It really puts us in turmoil
Former Plaid AM Brian Hancock
But he was told on Thursday morning that six AMs wanted him out.
At 1700 BST on Thursday he formally announced his resignation.
"I consider that it would be impossible for me to take forward the necessary changes without the support of at least a clear majority of group members," he said.
Dai Lloyd said he could not ignore the views of fellow Plaid AMs
Mr Jones said the changes needed in the party were so fundamental that he would have had to have strong support.
Plaid Cymru's parliamentary leader, Elfyn Llwyd, attacked his party's AMs for their role.
The Meirionnydd Nant Conwy MP said the leadership was just one of 25 issues to be discussed after the election and it was wrong to single out Mr Jones for the blame.
Former AM Brian Hancock, who lost his Islwyn seat last week, said it worsened the party's position and left it with no direction. "It really puts us in turmoil," he said.
Plaid MEP Eurig Wyn, speaking from Brussels, said news of the statement had caught him "totally unaware", but it was needed to "clear the decks".
Mr Wyn said the groundswell of opinion tended to point to the view that the party needed a new central leadership.
AM Dai Lloyd gave Mr Jones the news that half his group wanted him to go. Dr Lloyd said as chairman of the Plaid assembly group he could not ignore AMs' views or "sweep them under the carpet."
Helen Mary Jones could stand again for the leadership
His departure will lead to the second Plaid leadership contest within three years. Mr Jones, the Ynys Mon AM, won by a huge majority of party members in summer 2000, but there is no obvious successsor.
Possible candidates include AM Helen Mary Jones and MEP Jill Evans, who both contested the leadership three years ago.
Other potential candidates include MP Adam Price. Another MP, Elfyn Llwyd, is said to be "very doubtful" about running and a third, Simon Thomas, has said he will not stand.
Also ruling themselves out were former leader Dafydd Wigley, and AMs Janet Ryder and Dai Lloyd.
AM Rhodri Glyn Thomas expressed his interest in
becoming the party's leader at the assembly. But he said he would not want to be
president as well.
Mr Thomas wanted the two roles split and said it was an impossible
task to do both.
Mr Jones will remain both party president and leader of the assembly group until the leadership election.
The timetable will be discussed at a meeting of the party's executive on Saturday and the party hopes the new leader will be in place in time for the party's conference in September.
MP Adam Price may try to lead the party from Westminster
Plaid's number of assembly seats fell from 17 to 12 in last week's poll, a result which was was criticised as a "disaster" by his predecessor, Dafydd Wigley.
Mr Jones was elected leader by 77% of party members in summer 2000. But he ran into serious criticism over issues such as his party's alleged failure to safeguard the Welsh language in its so-called heartland areas in the north and west.
'I'm a fighter'
Ceredigion MP Simon Thomas had predicted the day after the last week's election that Mr Jones would face a challenge to his leadership.
But on the same day Mr Jones issued a defiant statement declaring: "I'm a fighter, not a quitter."
Plaid could now be plunged into a divisive leadership contest, with no obvious contender ready to take up the reins.
First Minister Rhodri Morgan expressed his sympathy for Mr Jones, and said the line between hero and zero was very fine.
He also said his only criticism was that Mr Jones could have chosen a better day from his point of view - as Mr Morgan had been announcing his cabinet throughout the day.