GAZA, March 26 (Reuters) - Hamas said its gunmen fired on Israeli soldiers who crossed into the Gaza Strip on Friday during a clash which Palestinian witnesses said inflicted at least one military casualty.

Hamas, Gaza's ruling Islamist movement, has largely held fire since its costly 2008-2009 war with Israel, though other factions have chafed at the de facto truce.

An Israeli army force raided 500 metres (yards) into Palestinian territory, and was confronted by our gunmen, said Abu Obeida, spokesman for the Hamas armed wing. This was our work, but was carried out for defence.

Witnesses said Friday's exchange of fire began when an explosion, possibly caused by a anti-armour rocket fired from the nearby Palestinian town of Khan Younis, hit an Israeli army patrol on the central Gazan border.

Backed by tanks, the troops fired back at their assailants and entered Gazan territory, the witnesses said. Such pursuits are common practice for the Israelis, who try to maintain a buffer zone within the border fence off-limits to Palestinians.

The witnesses said that, during the fighting, soldiers stretchered away a wounded comrade and helicopters came to the scene, apparently for medical evacuations.

Abu Obeida's statement did not make clear who might have carried out the initial ambush on the Israeli patrol. There were no other claims of responsibility, nor immediate word of Palestinian casualties.
An Israeli army spokeswoman said she was aware of an incident under way in the area. She did not offer more details.