RAMALLAH, West Bank - Yasser Arafat acknowledged today that the Palestinian Authority had made mistakes, but the rare admission appeared to be aimed more at deflecting criticism about his corrupt government than making real changes.

In a decade at the helm of the Palestinian Authority, Arafat has resisted attempts to get him to fight official corruption, reform the security services and relinquish some of his near-absolute powers. It was difficult to say how sincere he was in the vague comments in a televised speech to parliament.

"There were wrong practices in some institutions, and some misused their positions," he said. "There were not enough efforts to strengthen the rule of law, the independence of the judicial institutions ... Be we have begun measures to solve this."

In the Gaza Strip, meanwhile, Israel set off a mysterious explosion in an olive grove near the house of a senior Hamas activist early today, killing five Palestinians - at least four of them militants - and wounding seven. The main target of the attack, Hamas activist Ahmed Jabari, escaped with light injuries.

Arafat's speech comes amid growing dissatisfaction in the West Bank and Gaza Strip with his rule. Last month, street protests erupted over some of his appointments, and Arafat's prime minister briefly threatened to resign.

Even his harshest critics have not demanded Arafat resign - he is still widely considered as a national symbol and a guarantor of unity - but he was clearly rattled by the complaints.

In response, Arafat promised sweeping government reform and has met with lawmakers who asked him to put his pledges in writing. However, legislators have come away disappointed, saying Arafat has largely been evasive.

In his speech to parliament, Arafat acknowledged there is some official corruption, said those engaged in wrongdoing should be prosecuted and reiterated that he would streamline the security forces. However, he gave no specifics.

One of his harshest critics, former Cabinet minister Abdel Jawad Saleh, shouted that Arafat himself was protecting the corrupt. Arafat got angry, responding with an indignant question: "I'm protecting them?"

Saleh complained after the speech that Arafat is "not serious" about reforms and warned that there could be a nonviolent "Palestinian uprising against this authority very soon."