TEL AVIV, Israel — Israeli police on Monday said they were searching for six Palestinian prisoners who escaped from a high-security facility in northern Israel.

Police said they have erected roadblocks and are conducting patrols in the area.

The prisoners escaped from the Gilboa prison overnight, which is supposed to be one of Israel’s most security facilities, overnight. Such breakouts are extremely rare.

Israel’s Army Radio said the men escaped through a tunnel and appeared to have received some outside help. It said the prisoners included Zakariye Zubeidi, a former militant leader in the northern West Bank city of Jenin, as well as three Islamic Jihad militants serving life sentences for involvement in deadly attacks on Israelis.

The men were believed to have been headed for Jenin, where the internationally recognized Palestinian Authority wields little control and where militants in recent weeks have openly clashed with Israeli forces.