Ammon News - CAIRO (Reuters) - President Mohamed Mursi offered opponents a say in amending Egypt's constitution, but railed against "enemies" he accused of undermining the new democracy in a defiant speech ahead of mass protests planned to demand that he step down.

As the Islamist head of state ended a marathon televised address early on Thursday, liberals said they had heard nothing new, including any offer to include them in committees to draft institutional reforms and study "national reconciliation".

Opposition plans to stage a huge protest on Sunday, when Mursi completes a year as Egypt's first freely elected leader, were unchanged. After two people were killed in factional street fighting on Wednesday, the risk remains of a violent showdown, as Islamists also plan to rally in force.

Instability in the biggest Arab nation could send shocks well beyond its borders. It has long been an ally of the United States, which still funds Egypt's armed forces heavily.

The army, for decades the arbiter of Egyptian politics, has warned it may step back in to keep order. The head of the armed forces had a front-row seat in the audience for Mursi's speech in Cairo, which lasted nearly three hours.

General Abdel Fattah al-Sisi, who was promoted by Mursi, has warned feuding politicians that if they fail to forge consensus and violence runs out of control, then troops would intervene.

Mursi offered a diagnosis of Egypt's problems since the revolution of 2011 that, with military help, forced out Hosni Mubarak. "Political polarization and conflict has reached a stage that threatens our nascent democratic experience and threatens to put the whole nation in a state of paralysis and chaos," he said.

He acknowledged unspecified "errors" and promised reforms to help Egypt's fast-growing young population; he spoke of cutting unemployment and raising the minimum wage but blamed opponents for the instability that has driven the economy into crisis.

But unmoved liberal opponents mocked the length of his speech, his personal attacks on public figures and the cheering of the partisan audience seen on national television.

"Our demand was early presidential elections and since that was not addressed anywhere in the speech then our response will be on the streets on June 30," said Mahmoud Badr, the founder of the campaign to demonstrate on that date, the first anniversary of Mursi's inauguration. "I hope he'll be watching."

Badr, a 28-year-old journalist who launched a petition for Mursi's removal under the slogan "Tamarud-Rebel!", says it has gathered 15 million signatures in two months. "I feel ashamed that this man has become a president of my state," he said.

U.S. Secretary of State John Kerry, in Kuwait, said: "Egypt is historically a critical country to this region ... Our hope is that all those interested parties who are preparing to demonstrate will do so in a peaceful and responsible way, that builds the future of Egypt, doesn't tear it down."

"SABOTAGE"

Mixing anger and humor in his speech, Mursi drew cheers from Islamist supporters in the audience by slamming liberal opponents he said had rejected offers of dialogue and poured venom on "sabotage" by Mubarak loyalists who wanted to "turn back the clock".

"I took responsibility for a country mired in corruption and was faced with a war to make me fail," he said, naming senior officials, including judges and the former premier he beat in last year's election, as well as neighborhood "thugs". He also slammed some owners of hostile media, accusing one of tax fraud.

Two hours in, he offered an olive branch - an invitation to party leaders to meet as soon as Thursday to start work on an all-party committee to prepare amendments to the constitution.

Pushed through in a referendum late last year, the constitution has been a prime target of opposition complaints that Mursi's Muslim Brotherhood is using its ability to mobilize an organized electoral base to disregard the opinions of others.

Mursi also proposed a "national reconciliation" committee that would include Muslim and Christian clerics. Minorities and secular Egyptians worry he will subject them to Islamic laws.

Urging peaceful protests - and warning "violence will only lead to violence" - he urged opponents to focus on parliamentary elections rather than on "undemocratic" demands to overturn his election on the streets. "I say to the opposition, the road to change is clear," he said. "Our hands are extended."

OPPOSITION DEFIANT

Khaled Dawoud, the spokesman of the coalition of liberal parties that back the petition campaign, said Mursi's call for cooperation was not new and would not be taken seriously. "I am more determined than ever to go out on June 30 to demand the removal of an absolutely irresponsible president," he said.

"A boring speech that said nothing," concluded leftist former presidential candidate Hamdeen Sabahi.

A few thousand people milled around Cairo's Tahrir Square, the cradle of the revolution, many waving soccer-style red cards reading "Out!"

Ayman Anwar, a 55-year old computer engineer, stood with his wife Azaa staring at a screen on the traffic interchange set up to Mursi's speech.

"I didn't come out tonight to listen," he said. "I came out because I'm angry. No one could have imagined that this would happen to Egypt. We've replaced one dictator with another."

Before Mursi spoke, two people were killed and more than 200 were treated for injuries in the city of Mansoura, north of Cairo, when Islamist supporters clashed with their opponents.

Overnight, there were also skirmishes in Alexandria when youths approached a rally of Mursi supporters in the city.

Fears of a violent stand-off in the streets between Mursi's Islamist supporters and a broad coalition of the disaffected have led people to stock up on food. Long lines of cars outside fuel stations have snarled roads in Cairo and other cities.

Islamists plan a major rally in Cairo and some opposition groups say they, too, may take to the streets before Sunday.