* Protesters who helped oust Mubarak oppose army-backed rule
* Sisi close to announcing widely-expected presidential bid
* Nobel Prize Winner, activists deported en route to Gaza
By Noah Browning
CAIRO, March 5 (Reuters) - Egypt's April 6 protest group, which helped topple Hosni Mubarak in 2011, spoke out on Wednesday against any attempt by army chief Abdel Fattah al-Sisi to seek the presidency, saying this would be divisive and destabilising.
Field Marshal Sisi, who is also defence minister, told a military gathering on Tuesday he would soon begin official procedures for registering his candidacy because he could not "turn his back on calls by the majority of Egyptians".
April 6 at first backed Sisi's removal of Islamist President Mohamed Mursi in July, but, like some other secular groups, has since returned to its former stance opposing army-backed rule.
"The defence minister's candidacy for the post of president of the republic would not be in the interest of the divided nation and will not achieve the objectives of the revolution," April 6 said on its official Facebook page.
"Rather, it will increase the crisis greatly and detract from stability and desired progress," it said.
Opposition from April 6, which helped mobilise crowds against Mubarak, but has no broad political base, seems unlikely to dent Sisi's chances of sweeping to the presidency. No date for the election has been set.
Wildly popular, Sisi looks set to become the latest in Egypt's long line of rulers drawn from the military - a tradition only broken during Mursi's one year in power.
The army's overthrow of Mursi, Egypt's first freely elected leader, sharply divided the most populous Arab nation between those who supported it and Mursi's Muslim Brotherhood.
Security forces killed hundreds of pro-Mursi protesters while clearing their sit-ins in August - the bloodiest such crackdown in Egypt's modern history. Mursi and other Brotherhood leaders were detained, along with thousands of supporters.
Last year, the net spread to secular liberal activists who had initially supported the army's removal of Mursi, whom they accused of pursuing a narrowly Islamist agenda and of abusing his powers to ram through a religiously-oriented constitution.
Violating a strict new law against protests landed April 6's leader Ahmed Maher in jail in November.
Since an army-backed government replaced Mursi, Islamist militants based in the Sinai peninsula have waged a growing insurgency, attacking soldiers and police almost every day.
Authorities blame the Brotherhood for the violence and say one of its offshoots, the Palestinian Hamas movement, which rules the neighbouring Gaza Strip, is helping the militants - an accusation the Brotherhood and Hamas both deny.
Cairo airport officials have deported three international campaigners planning to travel to Gaza, which is under a tight Egyptian-Israeli blockade, on a humanitarian mission.
Mairead Maguire, a Nobel Peace Prize-winning peace activist from Northern Ireland, was turned away on Wednesday along with an American activist, the mission's spokesman said.
The day before, Medea Benjamin, an anti-war campaigner from the U.S. feminist group Code Pink was deported. She told Reuters by text message that police had broken her arm while she was in custody at Cairo airport. A security official there denied any abuse and said she had been on a watch list for threatening national security.
Egypt has declared the Muslim Brotherhood a terrorist group and a court on Tuesday banned all Hamas activities on Egyptian territory.
(Editing by Alistair Lyon)