Bombers killed a policeman and a soldier on Friday, hours before the start of campaigning for presidential polls which Egypt's former army chief who deposed an elected Islamist leader is expected to win.
Militants have unleashed a wave of attacks targeting security forces since the military ousted president Mohamed Morsi last July, while security forces have waged a deadly crackdown on Morsi's supporters and his Muslim Brotherhood movement.
Abdel Fattah al-Sisi, who ousted Morsi amid massive protests against his year-long rule, is the frontrunner in the election, with supporters viewing him as a tough leader who can restore order in the wake of a 2011 uprising which toppled Hosni Mubarak.
A bomb concealed in a traffic light struck a police kiosk near a courthouse in the northern Cairo district of Heliopolis, killing one policeman and wounding four others, the interior ministry said.
The attack came just hours after two suicide bombers attacked a checkpoint and a nearby bus outside the South Sinai provincial capital Al-Tur, security officials said.
A soldier was killed and six policemen were wounded by the first bomber, and five civilians were wounded by the second, the officials said.
In the first suicide attack, the assailant dressed in Bedouin garb approached the checkpoint, asked for directions and set off his bomb when soldiers asked him to leave, a military spokesman said.
Security forces have deployed in strength to protect the resorts along the South Sinai coast that are a major plank of the country's battered tourism sector.
Friday's bombings came a day before the start of official campaigning for the May 26-27 presidential election, in which leftist leader Hamdeen Sabbahi is Sisi's sole rival.
Sabbahi came third in the 2012 election which Morsi won, and he is seen by supporters as the only leader representing the aspirations of those who led the revolt against Mubarak in 2011, eventually forcing him from power after three decades of autocratic rule.
The prime minister's office said Friday's violence would not undermine Egypt's determination to hold "fair presidential and parliamentary polls".
Morsi's Brotherhood, which swept every election held after Mubarak's fall, is blacklisted as a "terrorist" organisation and said it will boycott the polls.
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- Morsi supporters, foes clash -
Morsi's ouster and the ensuing crackdown, which has killed more than 1,400 people since he was removed from office, have deeply polarised the country.
On Friday, two people were killed and three wounded in clashes between Morsi's supporters and civilian opponents near the Mediterranean city of Alexandria, the interior ministry said in a statement.
Clashes also erupted in Cairo, where security forces fired tear gas to disperse Islamist protesters, security officials said.
Police arrested 42 Morsi supporters across the country, the ministry said.
Top Brotherhood leaders, including Morsi, are behind bars and facing a flurry of trials.
The ongoing crackdown has also seen more than 15,000 Morsi supporters jailed, with hundreds sentenced to death in often speedy trials.
On Monday, a judge in the central city of Minya triggered a global outcry by sentencing to death 683 alleged Islamists, including Brotherhood chief Mohamed Badie, after just a 10-minute session.
Furious over the police crackdown on Morsi's supporters, militants have killed scores of soldiers and police in past months, mostly in the north of the rugged Sinai Peninsula.
But the jihadists have extended their reach to Cairo and the Nile Delta, carrying out a series of high-profile attacks in the heart of the capital.
The Al-Qaeda inspired Ansar Beit al-Maqdis (Partisans of Jerusalem) group has claimed the deadliest attacks, both inside and outside Sinai.
Another shadowy jihadist group, Ajnad Misr (Soldiers of Egypt), has claimed recent explosions in the capital, warning of more attacks against security forces.
The authorities say militants have killed around 500 people, most of them security personnel, in such attacks since July.