JERUSALEM (AP)_ Four prostitutes died Tuesday when a Tel Aviv brothel was torched, the latest attack in what police suspect is the work of a serial arsonist.

The four unidentified women apparently tried to escape from the apartment that served as a brothel but found the front door locked, Tel Aviv police said. The women inside a second brothel also set ablaze Tuesday managed to escape without harm.

The fires Tuesday follow similar attacks on two other brothels in the Tel Aviv area last week, said police commander Shlomo Aharonishky.

``We are pursuing a number of courses of inquiry, both the possibility of a dispute between operators of these businesses and also the possibility that extremist ultra-Orthodox Jews are responsible,'' Aharonishky told Israel Channel Two news. ``Every possibility is being examined.''

A gang of ultra-Orthodox Jews was behind a wave of arson attacks on erotica shops in Jerusalem in the 1970s, and in the mid-1980s, another gang set fire to billboards they consider offensive.

In Tuesday's attack, one woman was found in the hallway, another in the bathroom and two others died while hiding in a bedroom closet. The women died of smoke inhalation and burns, the police spokesman said.

The sex trade in Israel has boomed in recent years as thousands of women have flooded into the country, many lured from the former Soviet Union with false job promises as waitresses or dancers.

Once in Israel they are locked up in brothels, where they are forced to work as prostitutes. Tel Aviv has an estimated 100-150 brothels known to police, most of which are located in private apartments, Aharonishky said.

Russian-based crime gangs have used the influx of immigrants as a cover for sneaking in an estimated 10,000 prostitutes over the past decade.