Palestinians marked the fourth anniversary of their uprising Tuesday amid signs that the extremist Hamas group is preparing a political challenge to Yasser Arafat (search) despite a series of Israeli military blows at the movement's leadership.

Hamas published newspaper ads urging supporters to vote in upcoming municipal elections, saying "it's time for change." And a top Hamas (search) leader indicated the group might try to unseat Arafat in presidential elections, which have not yet been scheduled.

Meanwhile, Palestinians said a 22-year-old Hamas militant was killed in an exchange of fire with Israeli forces near the Jebaliya refugee camp. Gunmen took up positions to resist the Israelis, they said.

In other violence on Wednesday a wanted Palestinian man was killed in the West Bank city of Nablus when he tried to flee Israel troops who had come to arrest him, the army said.

Palestinians identified the man as Majdi Halifa, a member of the Al Aqsa Martyrs' Brigades, which is linked to Arafat's Fatah movement.

On Tuesday, Palestinian militants released an Arab-Israeli television producer for CNN a day after his abduction in the Gaza Strip. It remained unclear why he was taken hostage.

The kidnapping, coupled with Hamas' electoral challenge, were apt reflections of the state of affairs in the West Bank and Gaza Strip after four years of fighting with Israel. The violence has left Arafat's Palestinian Authority severely weakened, leading to widespread chaos and boosting Hamas' popularity.

"We need an evaluation of these four years," Palestinian Prime Minister Ahmed Qureia said. "Where have we been right and where have we been wrong? What did we achieve and what didn't we achieve?" Qureia also called on Israel to reassess its policies.

The uprising erupted on Sept. 28, 2000, after Ariel Sharon, then Israel's opposition leader, visited a sensitive Jerusalem hilltop revered by both Jews and Muslims. Palestinian riots broke out, and five months later Sharon defeated Ehud Barak in a special election for prime minister.

The fighting has taken a heavy toll on both sides, killing more than 3,000 Palestinians and nearly 1,000 Israelis.

In the latest violence, about 30 Israeli tanks moved into northern Gaza Tuesday night and fired several shells, witnesses said. The military said the purpose was to try to stop militants from shooting rockets at nearby Israeli towns. Earlier, the Israelis blew up a building next to the Gaza settlement of Netzarim, saying it contained a tunnel used by militants. No casualties were reported in either incident.

Israel appears to have gained the upper hand in the fighting. It has confined Arafat to his West Bank headquarters for three years and killed hundreds of leading militants. The Palestinian economy is in tatters.

In a sign of Palestinian weariness, a recent opinion poll by An-Najah University found that two-thirds of Palestinians support a cease-fire with Israel.

"The uprising has not been defeated, but it has not brought victory. Frankly, it is now closer to defeat than victory," commentator Hani al-Masri wrote in the Palestinian daily Al Ayyam.

Sharon has abandoned peace talks with the Palestinians and instead launched a "unilateral disengagement" plan meant to separate the two peoples. The plan includes building a huge barrier to separate Israel from the West Bank and making a complete pullout from Gaza next year.

Hamas is vying with other groups for a prominent role after the Israeli withdrawal from Gaza, where Hamas wields great influence despite Israeli assassinations of its top leaders.

On Tuesday, Hamas published newspaper ads urging its followers to register to vote in local Palestinian elections, which are scheduled to begin Dec. 9. "Fellow citizens, it's time for change. It's time to register your name," the ad said.

Hamas previously said it would participate in the elections, but until Tuesday it had shown minimal interest in the campaign.

The call came a day after a Hamas leader was quoted as saying the group planned to contest legislative and presidential elections, which Arafat has promised to hold but has not yet scheduled. The comment by Mahmoud Zahar marked the first time Hamas made such a commitment.

A strong Hamas campaign could pose a formidable challenge to Arafat. The veteran Palestinian leader consented this month to hold municipal elections in response to widespread discontent over his corruption-plagued government.

Arafat has long resisted elections, saying Israeli military occupation of the West Bank and Gaza Strip make orderly voting impossible. But critics accuse him of making excuses to avoid facing an electoral test of the growing dissatisfaction with his rule.

Hamas, which has carried out dozens of suicide bombings in Israel, is committed to the destruction of the Jewish state. Even so, Palestinian Authority officials welcomed Hamas' participation in the political process as a sign of moderation.

In Gaza, Palestinian militants released CNN producer Riad Ali.

It was not clear whether his kidnapping Monday signaled a new practice by Palestinian militants — perhaps an attempt to copy Iraqi insurgents who have snatched dozens of foreigners — or whether Ali was taken for personal or local reasons.

Talking to reporters after emerging from a Gaza police station, Ali refused to discuss what demands his abductors made, but said they identified themselves as members of the Al Aqsa Martyrs' Brigades, which is linked to Arafat's Fatah movement.

Al Aqsa spokesman Abu Mohammed denied the group was involved.