Kheldoun’s remarks to Ennahar television were another major setback Bouteflika, who hoped to pacify Algerians by promising to take steps to change the political landscape dominated by the president and the ruling elite for decades.
Bouteflika has reversed a decision to stand for another term after mass protests against his rule. He has been losing allies rapidly in recent days since returning from medical treatment in Switzerland.
Kheldoun, a former spokesman for the ruling party, became one of the most senior FLN officials to break with Bouteflika publicly.
He said the party had to look forwards and support the aims of demonstrators protesting against Bouteflika.
The FLN holds the majority in all elected assemblies, including parliament and local city councils.
Tens of thousands of Algerians have staged protests for weeks demanding a new era with younger leaders who would offer greater social freedoms and prosperity.
Bouteflika, 82, has rarely been seen in public since suffering a stroke in 2013, and the protesters say he is no longer in a fit state to rule. They took to the streets after Bouteflika, in office for 20 years, announced he would stand again, forcing him to reverse that decision this week.
A former minister who is familiar with Bouteflika’s inner circle told Reuters that the president could not survive given the pressure building against him from Algerians of all social classes.
“Game over. Bouteflika has no choice but to quit now,” the former minister said on condition of anonymity.
More mass protests are expected on Friday in the early afternoon after prayers.
Many Algerians say that the ailing president and other veterans of the 1954-1962 war of independence against France should hand over power to young technocrats who can focus on unemployment, poor services and stamping out corruption.
Although Bouteflika will not stand again and named a new prime minister, he stopped short of immediately stepping down. He intends to remain in power pending a national conference on political change and a new constitution.
But his position is becoming more tenuous as he has lost one ally after another, including prominent members of the FLN, which has dominated since France’s defeat in 1962.