By Marwa Awad and Yasmine Saleh

CAIRO (Reuters) - An Egyptian court threw the timetable for parliamentary elections into confusion on Wednesday, ordering the cancellation of President Mohamed Mursi's decree calling the vote and forcing a likely delay to polls due to start in April.

The Administrative Court's ruling deepened Egypt's political uncertainty at a time of social unrest and economic crisis, with the nation's foreign currency reserves at critically low levels and the budget deficit soaring.

The court said it had referred Egypt's amended electoral law, under which the lower house polls are due to be held, to the Supreme Constitutional Court for review.

Egypt has been torn by political confusion and strife since the 2011 uprising that deposed autocrat Hosni Mubarak. Many opposition parties had announced they would boycott the vote, which had been due to be held in four stages from April 22 until late June.

Mursi's office made no immediate comment on the ruling, handed down as the government says it wants to resume talks with the International Monetary Fund on a $4.8 billion loan to shore up Egypt's finances.

"It is now likely that elections will be postponed, extending political uncertainties and further delaying a possible IMF deal at a time when restoring confidence in the economy is needed to avert a potential economic crisis," said Farouk Soussa, chief economist at Citi in Dubai.

"Egypt's economic challenges are deepening by the day, while the prospects of addressing these seemingly diminish at an equally alarming rate," he said.

The Freedom and Justice Party, the party of Mursi's Muslim Brotherhood, said in a statement it respected the court's decision.

TECHNICAL GROUNDS

The court made its ruling on technical grounds, saying in a statement that the Shura Council, Egypt's upper house of parliament, had not returned the amended electoral law to the Supreme Constitutional Court for final review before passing it.

Egyptian courts have made a number of rulings that have gone against Mursi and his ruling Muslim Brotherhood. The previous Islamist-dominated lower house was dissolved by a court ruling that struck down the original electoral law under which the chamber had been elected.

Violence has frequently flared in Egyptian cities, notably late last year over a decree in which Mursi temporarily gave himself sweeping powers. Youths fought police in the Suez Canal city of Port Said for a fourth day on Wednesday.

Political science professor Mustapha al-Sayyid said a delay to the elections was likely as the case bounced between different courts.

"Of course the government will appeal but eventually, judging by previous experience, the higher court will rule to postpone the vote until the Constitutional Court sees the amended electoral law, which should have happened in the first place," he said.

Mursi called the elections on February 21. He has already changed the starting date to avoid making members of the Christian minority vote during their Easter festival.

Opposition politician Amr Hamzawy welcomed the court's decision. "Again, the judiciary has stopped the Muslim Brotherhood from making a mess of the rule of law and legislation," he told Reuters.

"Referring the law back to the Supreme Constitutional Court is a new lesson to the Muslim Brotherhood."

(Additional reporting by Sylvia Westall and Omar Fahmy; Writing by David Stamp; Editing by Andrew Roche)