CAIRO: UN chief Ban Ki-moon called for the release of Egypt's deposed president Mohamed Morsi as his supporters and the military who toppled him sought to defuse soaring tensions ahead of rival rallies Friday.

Ban demanded that Morsi and his high-level backers “be released or have their cases reviewed transparently without delay,” said deputy UN spokesman Eduardo del Buey.

Morsi and several Muslim Brotherhood leaders have been detained since the military drove him from power on July 3 in response to massive protests calling for his ouster.

Taking a step back after outraging Islamists and sparking concern in Washington, the military insisted on Thursday that it was not targeting Morsi's backers in calling for a mass rally to counter “terrorism and violence.”

Police said they were planning large-scale reinforcements to secure Friday's rallies, amid fears they could turn into a massive showdown between Islamists demanding Morsi's reinstatement and an array of opponents, including the military.

Egypt's military has set a 48-hour deadline, which expires late on Friday, after which it will decisively deal with “violence and terrorism,” according to a statement posted on a military-linked Facebook account.

Military chief Abdel Fattah al-Sisi had issued the deadline, it said, at the end of which, “the strategy for dealing with violence and terrorism will change... appropriately to deal guarantee security and stability.”

A senior army official told AFP the statement did not reflect the military's point of view, although it appeared on a “page with links to the armed forces.”

”The 48-hour ultimatum is a political invitation,” the officer said. “It doesn't mean after 48 hours we are going to crack down.”Hisham Qandil, prime minister before Morsi was pushed aside by the army on July 3, on Thursday proposed a three-stage roadmap that would start with confidence-building steps.

In a video recording posted on YouTube, the former premier said both sides should refrain from marches and hold rallies only in fixed locations.

No coup in Egypt, says US

The Obama administration told lawmakers that it will not declare Egypt's government overthrow a coup, officials said, allowing the United States to continue providing $1.5 billion in annual military and economic aid to the Arab world's most populous country.

William Burns, the State Department's No 2 official, held a closed-doors meeting Thursday with Senate and House of Representatives members just a day after Washington delayed delivery of four F-16 fighter jets to Egypt.

It was the first US action since the military ousted Mohammed Morsi as president, imprisoned him and other Muslim Brotherhood members and suspended the constitution earlier this month.

The administration has been forced into difficult contortions to justify not declaring a coup d'etat, which would prompt the automatic suspension of assistance programs under US law.

Washington fears that halting such funding could imperil programs that help to secure Israel's border and fight weapons smuggling into the Hamas-controlled Gaza Strip, among other things seen as critical to US national security.

Lawmakers said the administration hasn't characterized the upheaval as a coup, and may never do so, as it remains determined to continue providing Egypt with aid.

That assessment supported administration officials who said they weren't using that word to describe the power change and don't plan to as Egypt moves to restore civilian governance and holds new democratic elections.

Sen Bob Corker, the top Republican on the Senate Foreign Relations Committee, said legislators were looking at making the US coup law more flexible for similarly ambiguous cases in the future by adding waivers or conditions to help the administration.

But in Egypt's case, Corker conceded: ''It may never be determined what just happened.''

His counterpart on the Senate Armed Services Committee, Sen Jim Inhofe, also endorsed the idea of a waiver to give the administration the ability to call a coup what it is without facing automatic cuts.

Many from both parties in Congress sympathize with the administration's view and the need to back a military that has safeguarded Egypt's peace with Israel for three decades.

Still, some across the political spectrum disagree.

Republicans from libertarian Sen Rand Paul to hawkish Sen. John McCain, and Democrats such as Sen Carl Levin, have demanded the coup law be enforced.

The law stipulates, however, that it's President Barack Obama and his administration's decision on how to characterise Morsi's July 3 overthrow.

At the time, White House and State Department officials pointed to the large anti-Morsi protests that preceded the military's action and said Morsi's Islamist-led government, while democratically elected, was taking Egypt down an increasingly undemocratic path.

Since then, the president and his national security team have tried to balance support for the military's proposed return to constitutional rule and democratic elections alongside concern over the crackdown on key Morsi allies.

The Pentagon said this week the US was proceeding as planned with this year's joint military exercises.

The biennial maneuvers were canceled in 2011 following the revolution that ousted President Hosni Mubarak.

During Mubarak's three decades in power, Egypt was the United States' premier ally in the Arab world and at the heart of its efforts to fight Islamic terrorism, roll back Iranian influence across the Middle East and promote peace among Israel and its Muslim neighbors.