A Sinai-based Islamist militant group said on Wednesday it was behind a car bomb attack on an Egyptian police compound in the Nile Delta that killed 16 people and wounded about 140.
The army-backed government vowed to fight "black terrorism" after Tuesday's bombing in the city of Mansoura, saying it would not upset a political transition plan whose next step is a January referendum on a new constitution.
Ansar Beit al-Maqdis, or Supporters of Jerusalem, said Egypt's rulers were fighting Islamic legitimacy and had spilled the blood of oppressed Muslims. The police compound was a "nest of apostasy and tyranny", it said.
"We are continuing, God allowing, to fight them," the group said in a statement posted on an Islamist website.
The bombing increased fears that militant attacks, which have become commonplace in the Sinai peninsula since the army ousted Islamist President Mohammed Morsi in July following mass protests against him, are spilling into the rest of Egypt.
Attacks intensified after security forces killed hundreds of Morsi supporters and smashed their protest camps in Cairo in August. Morsi belongs to the Muslim Brotherhood, which denies any links to violence or to Sinai-based militant groups.
Ansar Beit al-Maqdis has claimed responsibility for several previous attacks, including a failed attempt to assassinate on the interior minister with a car bomb in Cairo in September. In 2012, the group said it had fired rockets at Israel from Sinai. It has also claimed at least 10 attacks in the past two years on a gas pipeline linking Egypt, Israel and Jordan.
Egyptian security forces arrested a Palestinian suspected bomber on Wednesday, the army spokesman said in a statement on Facebook.
He said the man, who lacked residency documents, had a Mercedes car with North Sinai number plates and had admitted that he had intended to blow it up in a "vital" security site.
The army spokesman said the man belonged to the Palestinian Islamist Hamas group, which rules the Gaza Strip, adjacent to Sinai, and said dozens of criminals, militants and Brotherhood politicians had also been detained after the Mansoura bombing.
Hamas denied any connection with the Palestinian, who the army spokesman identified as Joma Khamis Mohamed Breika.
"All these allegations are lies and fabrications," Hamas spokesman Fawzi Barhoum said, adding that the man was not listed in the civil register of Gaza residents. He urged the authorities in Egypt to "seek accuracy in their information and avoid mentioning Hamas in their internal affairs".
Authorities have filed charges against Morsi that include conspiring with Hamas, an offshoot of the Muslim Brotherhood, and militants in Sinai to organize military training camps, an accusation Hamas and the Brotherhood deny.
Separately, a member of the militant Al-Furqan Brigade was arrested in North Sinai, state news agency MENA said, citing an unnamed security source. The group claimed responsibility for attacking a ship in the Suez Canal in September.
Several civilians were wounded by gunmen near the town of Rafah on the border with the Gaza Strip, security sources said.
Late on Tuesday the authorities arrested a man they described as a Brotherhood leader on suspicion of involvement in the Mansoura attack, security sources and state media said.
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