A bomb explosion wounded four people overnight at a rally in Cairo for presidential election frontrunner Abdel Fattah al-Sisi, Egyptian security officials said on Sunday.
Two policemen were among those hurt in the attack, the first targeting a rally since campaigning began two weeks ago for the May 26-27 election, said the officials.
The bomb had been planted in the ground under a tent that hosted the gathering in support of Sisi, who himself was not present when the device exploded.
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Sisi, who is widely expected to trounce his only rival, leftist leader Hamdeen Sabbahi, has not addressed any public rallies so far during the campaign.
The former army chief led the ouster of Islamist president Mohamed Morsi in July last year, after massive protests against his single year of turbulent rule.
Since then, the authorities have been waging a crackdown on Morsi's now-banned Muslim Brotherhood in which more than 1,400 people have been killed and 15,000 arrested.