The alleged ringleader in the killing of two Palestinian policemen has died in custody after being beaten by security forces, a senior local official said on Tuesday.

The officers were killed in the West Bank city of Nablus last week when gunmen opened fire on security forces.

Two of the gunmen died in the subsequent shootout.

Ahmed Halawa, the alleged leader of the attackers, was arrested by police overnight and taken to the city's Jneid prison, Nablus governor Akram Rajub told the official Palestinian news agency WAFA.

Once there, he was severely beaten by security personnel, lost conciousness and later died, Rajub said.

‘We'll examine the incident and draw lessons from it,’ he said.

Hamas, which runs the Gaza Strip and is a bitter rival of the Fatah-run Palestinian Authority ruling the West Bank, condemned Halawa's ‘execution’.

It said it showed ‘the bloody nature of the Palestinian Authority's security services.’

Hamas and Fatah are due to contest municipal elections across the Palestinian territories in October.

Amnesty International has accused Palestinian security forces of routinely mistreating prisoners, with torture common and committed with impunity.

Under the 1993 Oslo accords with Israel, Palestinian police are only authorised to operate in 18 percent of the occupied West Bank, encompassing most of the major Palestinian towns, including Nablus.

The northern West Bank has seen a number of Palestinian police raids in recent months. The area has witnessed factional infighting within the ruling Fatah movement of Palestinian president Mahmud Abbas.