Israeli troops poured into the West Bank town of Nablus on Thursday, sparking clashes and makeshift bomb attacks that left five soldiers wounded, security sources said.

Around 80 army jeeps rolled into the Old City in the heart of historic Nablus, opening fire at random, conducting house-to-house searches and blowing open front doors, according to Palestinian witnesses.

The Israeli military said an officer and a soldier were severely wounded, and two others lightly hurt, when Palestinians blew up a makeshift bomb while troops were operating in Nablus, which began overnight.

"Another IDF officer was moderately wounded when Palestinians activated an explosive device in a separate incident overnight," it added.

"Throughout the operation Palestinians activated a total of six explosive devices and opened fire in two different incidents at IDF forces in Nablus."

Two suspected militants from Palestinian president Mahmud Abbas's Fatah party were arrested and weapons confiscated, the army said.

The Al-Aqsa Brigades, an armed group linked to Fatah, issued a statement claiming resonsibility for throwing explosive devices at Israeli troops.

Local Palestinian sources said several suspects were arrested but were unable to specify a precise number.

The Israeli incursion prevented dozens of Palestinian pupils in the Old City from attending an end of school exam scheduled on Thursday.

Thursday's operation came one day after 12 Palestinians were killed in twin Israeli operations in the Gaza Strip.

"We condemn the Israeli military operation ongoing in Nablus and which was launched shortly after those in Gaza," said Prime Minister Salam Fayyad during a meeting with religious leaders in Ramallah.

"Here we see an Israeli attempt to sabotage our efforts towards restoring security," he added.