GAZA CITY, West Bank (AFP) - Palestinian Authority president Mahmud Abbas was Friday locked in a battle of wills with the Hamas government, revoking its decision to create a new security force of armed militants.

The head-on collision sent tensions soaring between the moderate Palestinian leader and the radical Islamists, marking the first time Abbas has revoked decisions by the Hamas government since it was sworn in last month.

Abbas has ultimate responsibility for security, which has become a key battle ground between Hamas and Abbas and added to the pressure of a serious fiscal crisis in the government compounded by international aid cuts.

"President Abbas considers the decisions of interior minister Said Siam illegal and anti-constitutional, and he has sent a letter to this effect to prime minister Ismail Haniya," Tayeb Abdelrahim told reporters.

On Thursday, Siam announced he was creating a new security force of volunteer gunmen from armed factions to supplement the work of Palestinian police and security forces faced with rampant chaos in the territories.

At the same time he nominated top Gaza-based militant Jamal Abu Samhadana to a senior position in the interior ministry to oversee various security elements, including the new force.

The Palestinian Authority was left fuming after being given no prior notice of the unilateral proclamations.