GAZA CITY: Hamas accused Palestinian president Mahmud Abbas on Saturday of usurping power after he called presidential and legislative elections for January.

Abbas, whose term expired in early 2009, "must be tried for usurping power," deputy Palestinian parliamentary speaker Ahmed Bahar told a news conference in the Hamas-ruled Gaza Strip.

Late on Friday, Abbas decreed elections be held on January 24, in a move seen as turning up the heat on Hamas to sign an Egyptian-brokered deal for Palestinian unity.

Hamas spokesman Fawzi Barhum swiftly rejected the move, branding it illegal and unconstitutional.

The decree calling elections "has no value whatsoever from a constitutional point of view," Bahar said, noting that Abbas's tenure expired in January.

Abbas was elected on January 9, 2005, for a four-year term. The Palestinian Authority extended his presidency by one year so that the next presidential and parliamentary elections could be held on the same date.

Hamas has consistently rejected the extension granted to Abbas and does not consider him the legitimate president of the Palestinian people.

The Islamist Hamas and the secular Fatah faction led by Abbas have been at loggerheads for years.

Simmering divisions boiled over in June 2007 when Hamas fighters expelled Abbas loyalists from Gaza in a week of bloody clashes, seizing control of the impoverished and densely populated territory.

In the last parliamentary elections in January 2006, Hamas won an upset victory over the previously dominant Fatah.