Egypt's Islamist president fired the first volley Sunday in his battle with the nation's powerful generals, calling on the Islamist-dominated parliament to reconvene despite a military-backed court ruling that dissolved it.

A week into his presidency, the surprise move by Mohammed Morsi threatened to plunge the country into a new bout of instability and violence, nearly 17 months after the ouster of authoritarian leader Hosni Mubarak.

"This is the start of a battle that has for some time been brewing," said Negad Borai, a prominent rights lawyer and activist. "In this battle, the military may be the weaker opponent since it is up against an elected president."

Morsi's decree appeared to catch the generals off guard. In the first sign of an imminent crisis, the Supreme Council of the Armed Forces held an "emergency meeting" shortly after it was announced. The official Middle East News Agency said the generals met to "review and discuss the consequences" of the decision.

The Supreme Constitutional Court, the tribunal that dissolved the legislature last month, was to meet Monday to discuss the issue.

Morsi, a member of the powerful Muslim Brotherhood, which has long been at odds with the military, also called for new parliamentary elections within 60 days of the adoption of a new constitution, which is not expected before late this year.

The dual moves were seen as a significant step by a leader whose authority was called into doubt by the generals' power grab in the days before and after the June 16-17 presidential runoff.

Last month, the then-ruling military generals dissolved the legislature after the Supreme Constitutional Court, the country's highest tribunal, ruled that a third of its members had been elected illegally — a move that angered the Brotherhood and poisoned the atmosphere ahead of the military's handing over of power to Morsi on June 30.

The dissolution of parliament came as a severe blow to the Brotherhood, which held nearly half its seats and has dreamed of political power for most of its 84 years in existence. Long banned, the group's leaders and hundreds of its supporters were jailed in the 1950s and 1960s, and subjected to repeated crackdowns throughout most of Mubarak's 29 years in power.

While Morsi made no mention of the court ruling, taking aim only at the generals in revoking the military decree disbanding the legislature, some questioned whether he had the legal authority to overrule the high court.

The country's leading pro-reform campaigner, Nobel Peace Prize Laureate Mohamed ElBaradei, himself a longtime critic of the military, warned that Morsi's action threatened to undermine the country's judicial authority.

The president's decree, he wrote on his Twitter account, "ushered Egypt into a constitutional coma and a conflict between the state's branches."

With the constitution in effect under Mubarak suspended, and no new one in place because of disputes over who should write it, Morsi's decree drew attention to the disarray over the roles and powers of Egypt's governing institutions.

The military announced a "constitutional declaration" last month giving itself legislative powers in the absence of parliament and stripping Morsi of much of his presidential authority. The generals also took control over the process of drafting a new constitution, as well as control over the national budget.

Morsi came to power after narrowly defeating Mubarak's last prime minister, Ahmed Shafiq, in the runoff last month. Declared the winner June 24, he symbolically took the oath of office five days later at Tahrir Square, birthplace of the revolt that toppled Mubarak's regime on Feb. 11, 2011.

He took the formal oath the next day before the Supreme Constitutional Court and again at Cairo University before hundreds of his supporters, including many of the dissolved legislature's lawmakers. In his inauguration speeches Morsi hinted at his displeasure over parliament's dissolution and his own diminished powers, pointedly seating the speaker of the disbanded parliament, Saad el-Katatni of the Brotherhood, in the front row during the Cairo University ceremony.

Several hundred Morsi supporters gathered in Tahrir on Sunday night to celebrate his decision.

Morsi's move to reopen parliament came just hours after a meeting in Cairo with a senior U.S. official, who delivered a message from President Barack Obama assuring him of America's commitment to a "new partnership" with Egypt.

White House officials said Obama hoped to meet with Morsi during the U.N. General Assembly meetings in New York in September.

U.S. Deputy Secretary of State William Burns told reporters that Egyptians could rely on U.S. support as they try to realize their aspirations.

"Egyptians know far better than we do that their aspirations are not yet fully realized, but they can count on America's partnership on the complicated road ahead," Burns said.

Obama also invited Morsi for talks in the White House in September, Egypt's state television said.