A new militia loyal to Palestinian head Mahmoud Abbas has taken up positions in the West Bank town of Jenin.
This comes a few weeks after the Hamas-led government deployed its own new force in Gaza.
The commander of the new militia said it would support the official forces. But the Hamas deputy PM Nasser Shaer has denounced it as “unacceptable”.
Correspondents say the creation of the militia is likely to worsen tensions between Hamas and Mr Abbas’ Fatah.