Hours later it was announced that former minister Al-Baji Ca'ed al-Sebsi would take over the premiership. Al-Sebsi was foreign minister under Habib Bourguiba, Tunisia's president after independence,
Ghannouchi made the announcement on state television on Sunday, saying that he had thought carefully before taking the decision and that he had the support of his family.
"I am not running away from responsibility ... This is to open the way for a new prime minister," he said. "I am not ready to be the person who takes decisions that would end up causing casualties."
Ghannouchi has led Tunisia since former president Zine El Abidine Ben Ali fled the country on January 14 following a popular uprising.
But Ghannouchi was a longtime ally of Ben Ali and, though he pledged elections to be held by mid-July, protesters have called for him to step aside.
"He's been under real pressure since he took over, and that pressure increased in the past 48 hours," said Nazanine Moshiri, Al Jazeera's correspondent in Eastern Tunisia.
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