CAIRO (Reuters) - Egyptian President Abdel Fattah al-Sisi appointed a new armed forces chief of staff on Saturday, and the interior ministry dismissed several high-ranking officials in an apparent reorganization of the country s security command. No reason was given for the reshuffle, but the interior ministry decision came a week after a deadly attack on a police operation in a western desert area of Giza Province, in which the ministry said 16 police were killed after coming under heavy fire. Egyptian forces have been fighting several armed Islamist groups, mostly in the northern part of the Sinai peninsula, since Sisi helped lead the military overthrow of President Mohamed Mursi of the Muslim Brotherhood in 2013. Hundreds of members of the security forces have been killed in attacks by militants in recent years. A local Islamic State affiliate has been the main foe of the security forces in the north Sinai.   A statement from the presidency said Gen. Mohamed Farid Hegazy would replace Gen. Mahmoud Hegazy, who has been made the president s adviser for strategic planning and crisis management.  In a separate statement, the interior ministry announced that it had replaced several high-ranking officials, including the head of homeland security, assistant to the minister for security in Giza province, the director of Giza s security and director of operations for central security.  It gave no further details on the shakeup. No militant group has yet claimed responsibility for last week s attack on the police in a remote desert area of Giza, about 130 km (80 miles) southwest of the capital Cairo.     Thirteen militants were killed in a raid on a farm hideout in the region on Friday. State news agency MENA quoted a security official as saying it was  revenge for the blood of the men who were martyred last week in the oasis . The vast western desert region has always been a security headache with arms flowing across the frontier with Libya, where militant groups have found shelter since the country fell into chaos after the 2011 end of Muammar Gaddafi s rule. Sisi is a former military commander elected by a landslide in 2014 and presents himself as a bulwark against Islamist militancy. He is widely expected to run for re-election next year.  