WASHINGTON — Fearing a political-military implosion that could throw its most important Arab ally into chaos, the Obama administration has abandoned its hands-off approach, delivering pointed warnings to the three main players in the crisis: Muslim Brotherhood President Mohammed Morsi, protesters demanding his ouster and the powerful Egyptian military.

U.S. officials said Tuesday they are urging Morsi to take immediate steps to address opposition grievances, telling the protesters to remain peaceful and reminding the army that a coup could have consequences for the massive American military aid package it receives.

The officials said Washington has stopped short of demanding that Morsi take specific steps, but has instead offered strong suggestions, backed by billions of dollars in U.S. aid, about what he should do to ease the tensions.

Those include calling early elections, firing an unpopular prosecutor and expressing a willingness to explore constitutional change. The army has been told that the $1.3 billion in foreign military financing it receives each year from Washington could be jeopardized by a coup or the appearance of a coup.

President Barack Obama personally delivered the message to Morsi in a phone call late Monday from Tanzania where he was wrapping up a trip to Africa, the officials said. Around the same time, Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, called his Egyptian counterpart to point out that U.S. law requires cuts in military assistance in most cases when a country’s armed forces are involved in an unconstitutional change in government, the officials said.

Meanwhile, diplomats at the U.S. Embassy in Cairo have been speaking with the opposition, the officials said.