Saudi Arabia is emerging at the forefront of a forceful effort by Persian Gulf monarchies to back Egypt's new military leaders, exacerbating a fierce struggle for influence in the chaotic and increasingly leaderless Arab world and putting the Saudis at odds with the U.S., a long-standing ally.

On Monday, Saudi Arabia promised to compensate Egypt for any aid that Western countries might withdraw in response to the harsh tactics employed by Egypt's leaders to quell protests by supporters of deposed President Mohammed Morsi, in which nearly 1,000 people and more than 100 police are reported to have been killed over the past week.

Saudi Arabia is already the largest contributor to a $12 billion aid package pledged by Persian Gulf countries since the July 3 coup that ousted Morsi, dwarfing the $1.5 billion in annual U.S. aid that congressional leaders are pressuring the White House to suspend.