TUNIS (Reuters) - Tunisian President Zine al-Abidine Ben Ali, bowing to pressure from the worst unrest in decades, said on Thursday he would not seek a sixth term in office.

A leading opposition figure welcomed the pledge from Ben Ali, who has been head of state for more than 23 years, and called for the immediate creation of a coalition government.

* Will this stop the unrest? Early indications were that Ben Ali’s decision, announced in an emotional and contrite televised address, had been positively received.

Witnesses said hundreds of people -- ignoring a curfew -- poured into the streets to celebrate in the Lafayette area of the capital, which just hours earlier had been the scene of violent clashes with police.

* However, there is a risk that the people who have been involved in the weeks of protests will now view Ben Ali as a weakened lame duck and decide to press their advantage by continuing the unrest.

Signals from the interior of the country, the protest movement’s heartland, on whether people there are appeased by Ben Ali’s promise, will be crucial.

* It is not at all clear who will replace Ben Ali when he steps down. He has dominated the country’s political landscape for so long that there are no obvious candidates.

Some analysts had said his son-in-law, Sakher Materi, was being groomed for the succession but after the unrest anyone from Ben Ali’s inner circle is not likely to be welcomed by voters.

The opposition is weak and divided and parts of it are perceived as being the puppets of the government. Najib Chebbi, founder of the PDP party, is viewed by Western diplomats as the most credible of the opposition leaders. Others are in exile in France.

A test of whether Ben Ali is sincere about change will be whether they are able to come back. Other candidates could emerge from inside the administration: there are some technocrats in government who may be acceptable to Ben Ali’s supporters and opponents.

* Ben Ali is 74 and there will be questions about whether he will want to continue in office until 2014 or if his health will permit him to do that. Some Western diplomats say they believe he is suffering from serious health problems, though officials have denied that.

* The army and military are influential in their own right in Tunisia and it is likely they will go along with Ben Ali’s climb-down.

There had already been indications they were uncomfortable with the building confrontation with protesters. Witnesses in at least two towns said on Thursday that police had vanished, while opposition activists had said senior army chiefs were refusing to fire on protesters.