– Two of the Persian Gulf's richest monarchies pledged $8 billion in cash and loans to Egypt on Tuesday, a decision that was aimed not only at shoring up a shaky transitional government but also at undermining their Islamist rivals and strengthening their allies across a newly turbulent Middle East.

The robust financial aid package announced by Saudi Arabia and the United Arab Emirates came a day after the Egyptian military killed dozens of Muslim Brotherhood members protesting last week's military ouster of Egypt's Islamist president, Mohammed Morsi. The aid package underscored a continuing regional contest for influence between Saudi Arabia and Qatar, one that has accelerated since the Arab uprising upended the status quo and brought Islamists to power.

Qatar, in alliance with Turkey, has given strong financial and diplomatic support to the Muslim Brotherhood but also to other Islamists operating on the battlefields of Syria and, before that, Libya. The Saudis and Emiratis, by comparison, have sought to restore the old, authoritarian order, fearful that Islamist movements and calls for democracy would destabilize their own nations.

The promise to provide so much assistance also highlighted the limits of U.S. leverage: The United States provides Egypt $1.5 billion in annual aid, a fraction of what the gulf states have promised. But the gulf intervention contrasted sharply with the Obama administration's uncertainty about how to respond to last week's military takeover and, more broadly, how to wield influence across an increasingly chaotic and fragmented Arab world where U.S. interests are hard to define.

The White House has said it is reviewing the circumstances of the military takeover before making a decision on the annual aid to Egypt — which some in Congress, notably Sen. John McCain, R-Ariz., have said should be suspended, calling the takeover a coup d'état. But Tuesday, the White House spokesman, Jay Carney, struck a somewhat different tone, saying the administration was encouraged by the timetable provided by Egypt's interim authorities for a transition to elections.

The Saudis and Emiratis were nearly buoyant at the military's move to oust Morsi. Both are hostile to the Brotherhood's Islamist-cum-democratic agenda, which they see as a threat both to their own monarchical legitimacy and to regional stability. Qatar, by contrast, provided about $8 billion in aid to Morsi's government during his yearlong tenure, and Turkey offered loans of $2 billion.

The tensions between Qatar and Saudi Arabia are older and broader than the Arab uprisings that began in 2011. Saudi Arabia, which prefers to work its checkbook diplomacy quietly and behind the scenes, sees itself as the regional leader. But the Qataris have for years fashioned a outsize foreign policy, often rebuffing Saudi Arabia's perceived interests, using its wealth and Al Jazeera, the television network it built, to play a decisive role in some of the region's most volatile and important events.

Qatar, host to the largest U.S. military base in the Middle East, has also eagerly funded Islamists in Tunisia, Libya, Syria and Egypt, often siding with the Muslim Brotherhood or its affiliates, like Hamas. Suddenly, some of the tables have turned on Qatar.

With the rise of the Brotherhood, the Saudis had largely cut off aid to Morsi's government and ignored U.S. requests to help Egypt manage a worsening economic crisis. After Morsi was ousted by the Egyptian military last week, the Saudi and Emirati governments were quick to issue strong statements of support for the transition. "This is clearly a setback for the ideology that Qatar and Turkey support and encourage," one Arab official said. "If political Islam was a stock, it would have gone down dramatically over the past week."