* Brushes aside suggestion from Muslim spiritual leader
* Boko Haram main threat to Africa's top oil producer
* 13 Christians killed in Kano at weekend, group says (Recasts, adds killings of Christians in Kano, detail)
MAIDUGURI, Nigeria, March 7 (Reuters) - Nigeria's President Goodluck Jonathan said he was not ready to offer an amnesty to members of Islamist militant sect Boko Haram, brushing aside a proposal from the country's most senior Muslim spiritual leader.
Jonathan spoke on his first state trip to the northeastern region worst hit by the group's more than three-year insurgency - the Christian southerner has been widely criticised for not visiting sooner.
"I cannot talk about amnesty with Boko Haram now until they come out and show themselves," Jonathan told reporters in Yobe state capital Damaturu, a town regularly hit by the sect's guerrilla-style bomb and gun attacks.
Muslim leader the Sultan of Sokoto suggested this week members of Boko Haram - who currently pose the country's biggest security threat - should be offered an amnesty, similar to the one given to militants in the oil-producing Niger Delta in 2009.
The delta deal promising no prosecution and cash for fighters who handed in their weapons pulled thousands of armed youths out of the creeks.
It almost wiped out militant attacks on oil pipelines for political purposes, which had choked off Africa's biggest oil industry.
"Some people are comparing Boko Haram with the Niger Delta but, in Niger Delta if you call them (the militants), they will come out. But the Boko Haram don't and we can't grant amnesty to ghosts," Jonathan said during his one day visit.
Boko Haram has operated under a cloak of secrecy since it started its campaign to carve out an Islamic state in Africa's largest oil producer - a country split roughly equally between Christians and Muslims.
Since the killing of Boko Haram's spokesman last year, members have stopped calling to claim attacks. In recent months, bombings and shootings have been attributed to Boko Haram by the army or police.
The government has accused politicians in some areas of backing the insurgency, while some analysts say Boko Haram is a label used by a collection of armed groups, rather then one coherent organisation.
Criminal gangs have also sprung up, hoping their robberies and raids will be blamed on the militants.
The sect has regularly targeted soldiers, police, government officials and Christians.
At least 13 Christians were killed last weekend by suspected Islamist gunmen in a suburb of Kano, the north's biggest city, the head of the Christian Association of Nigeria Ransom Bello told a news conference on Thursday.
Kano state Police Commissioner Musa Daura confirmed the attack, but put the death toll at eight.
Boko Haram's self-proclaimed leader Abubakar Shekau appeared in a video circulated on Sunday rejecting any notion of a ceasefire or peace talks with the government.
Western governments fear Boko Haram, or factions of it, have linked up with other groups in the region, including al Qaeda's North African franchise.
Attacks on foreign targets have become more common, especially since a French-led operation last month against Islamists in northern Mali. Nigeria has sent hundreds of troops there to join the operation. (Reporting by Ibrahim Mshelizza; Additional reporting by Chukwuemeka Madu in Kano; Writing by Joe Brock; Editing by Tim Cocks and Andrew Heavens)