Mr Yasser Arafat's Palestinian Authority appears to have declared a mini-war on its Islamic rival, the militant Hamas movement. About 200 Hamas activists are believed to have been arrested by the Authority in the past few days, including several of the group's most prominent leaders.
The Gaza offices of Reuters have also been closed down, presumably by the Authority to protest at the efficiency with which the news agency publicises Hamas communiques.
Israel has been urging Mr Arafat for years to crack down on Hamas activities. But the move now has less to do with Israeli pressure than with the intensifying competition between the Authority and Hamas for the support of Palestinians. Hamas is believed to have the support of up to a quarter of Palestinians.
The rivalry has reached its peak in the past two weeks, following the death of the "Second Engineer," Hamas's bomb-maker, Muhi a-Din a-Sharif. The Authority claims that Sharif was murdered by a fellow Hamas militant, Mr Imad Awadallah, who was captured in Ramallah at the weekend. Hamas officials insist that either the Authority, or Israel acting with its support, were responsible. Hamas leaders have been publicly critical of the Authority, accusing it of helping Israel do its dirty work. In response, the Authority has been rounding up key Hamas figures, including the movement's spokesman, Mr Abdel Aziz Rantisi.
The Authority has carried out similar mass arrests in the past - but only in the wake of Hamas suicide bombings. And it has generally released most of those detained after just a few days.
Despite the tension, Hamas threats to avenge Sharif's death remain concentrated on Israel. Indeed, at a stormy Hamas rally in Sharif's memory, held on Saturday in Nablus, a model of an Israeli bus was symbolically set alight.
AFP adds: Some 30,000 Israelis defied pacifist protesters and possible attacks by Islamic militants yesterday to join Jewish settlers in Hebron for a celebration of Israel's 50th anniversary.
The Israeli army deployed reinforcements around Hebron's Jewish enclave and allowed only Jews to the site of the rally next to the Cave of the Patriarchs, a holy place for Jews and Muslims alike.
Several hundred Israeli peace activists tried to disrupt the rally but were barred by police from entering the city, witnesses said.