The open-ended ceasefire was to allow time for negotiations to end the showdown between al-Sadr's al-Mahdi army and a joint Iraqi-US force, Shaikh Ahmad al-Shaibani said.
Talks are taking place between the occupation forces, Iraqi security troops, the government's pointman on security, Muwafaq al-Rubaai, and close al-Sadr aide Shaikh Ali al-Sumaisim, he added.
The week-long offensive on Najaf caused outrage throughout Iraq and much of the Arab world as protesters took to the streets and voiced resentment of the heavy-handed approach of US-led occupation forces in and around the city.
On Friday, a slightly wounded al-Sadr from early morning US shelling of Najaf demanded the resignation of the Iraqi interim government, calling it "dictatorial" and saying it was worse than the Baathist government of Saddam Hussein.
On the negotiating front, US Secretary of State Colin Powell said representatives of al-Sadr and the Iraqi interim government were talking about a ceasefire in Najaf. The US wanted the fighting to end, but was deferring to the Iraqi government, he said.
The US military, meanwhile, said it had suspended offensive operations against al-Sadr's fighters, who are holed up in the city's vast cemetery and the Imam Ali shrine, one of the holiest sites to Shia Muslims.
Powell said, "We do not in any way wish to get involved with the mosque. It's a very holy place for all Shia."