By Tom Perry and Alastair Macdonald
CAIRO (Reuters) - Islamist supporters of Egyptian President Mohamed Mursi will rally in Cairo on Friday in a show of approval for him to upstage opposition protests planned to mark his first year in office at the end of the month.
Preparations for renewed street action after some months of calm have raised fears of violence of the kind that has punctuated the two-and-a-half years since Hosni Mubarak fell.
Mursi's opponents, who say at least 13 million people have signed a petition calling on him to step down, hope protests on June 30 will force him out. Their demand has angered Islamists who see it as an undemocratic bid to remove an elected leader.
His allies will rally after Friday prayers in Cairo.
A year after Mursi won election - with 13.2 million votes - the split between his supporters and a diverse opposition that accuses his Muslim Brotherhood of trying to Islamise the state is deeper than ever. It has fuelled political instability that is hampering Egypt's recovery from a deep economic crisis.
Tensions between Mursi's supporters and opponents spilled over into violence outside Cairo this week. Around 100 people have been injured in scattered skirmishes triggered by Mursi's decision to appoint more Islamists as provincial governors.
Rhetoric has grown more toxic in recent days: one Islamist cleric referred to Mursi's opponents as "infidels" during a rally attended by the president last week. The opposition are billing it as Mursi's last days in office, hoping for a repeat of the January 25 uprising that toppled Mubarak in 2011.
"There are numerous saboteur forces which aim to bring down the state," said Khaled al-Sherif of the political wing of al-Gamaa al-Islamiya, a once armed Salafist group that backs Mursi.
But Egypt's biggest Salafist force, the Nour Party, is not taking part. It has warned of "an imminent collision" between Egyptians and called on both sides to give ground - Mursi by appointing a cabinet for national unity and the opposition by switching its focus to elections from street protests.
Grievances have been stirred by economic hardship as the Mursi administration has struggled to attract foreign tourists and investment, confront a budget crisis and stem a slide in a local currency now at record lows against the dollar.
Islamists say the opposition have rebuffed Mursi's offers of power-sharing and want to thwart him by fomenting instability.
"My real worry is that tomorrow will be another round of spreading hatred: accusations of being infidels and being against Islam," said Khaled Dawoud, spokesman for the National Salvation Front, an alliance of liberal and leftist parties.
Along with Mursi and the Brotherhood, one less obvious target of the wrath of some protesters is the United States and, specifically, its ambassador to Cairo, who this week suggested they would do better to improve opposition organizations than risk violence trying to oust a president who was fairly elected.
In a speech on Tuesday, Anne Patterson responded to "conspiracy theories" among disappointed liberals that Washington secretly backed a Brotherhood takeover of Egypt.
"This is the government that you and your fellow citizens elected," she said. "Even if you voted for others, I don't think the elected nature of this government is seriously in doubt.
"Egypt needs stability to get its economic house in order, and more violence on the streets will do little more than add new names to the lists of martyrs. Instead, I recommend Egyptians get organized."
Prominent businessman Naguib Sawiris shot back on Twitter: "Madam Ambassador, ... Please bless us with your silence."
Other social media postings were less polite. And the National Association for Change, among the organizers of the June 30 rallies, issued a statement complaining of Patterson's "blatant interference" in Egyptian domestic affairs.
(Additional reporting by Shaimaa Fayed and Omar Fahmy; Editing by Mark Heinrich)