Olmert is criticised for suggesting peace talks with the Palestinians.
Olmert’s office has protested their release to Abbas. But Tawfiq Tirawi, the Palestinian intelligence chief, denied they were freed.
An Israeli government spokeswoman had no immediate information on the assassination attempt, and it was not clear how close the plotters got to carrying out the plot.
It also was not clear why Israel waited two and half months to disclose the alleged assassination plan.
While Abbas oversees the official Palestinian security forces, he has little control over pro-Fatah armed groups, which frequently act counter to his efforts to reconcile Israel and the Palestinians.