(CNN) -- Former Nigerian President Olusegun Obasanjo has said more could be done to reach out to the militant Islamist group Boko Haram to find out what leads it to carry out acts of violence.

In an interview with CNN, Obasanjo suggested the current government should adopt a dual-track approach rather than just cracking down on the group.

"To deal with a group like that, you need a carrot and stick. The carrot is finding out how to reach out to them," he said. "When you try to reach out to them and they are not amenable to being reached out to, you have to use the stick."

Obasanjo said President Goodluck Jonathan was "just using the stick" in his efforts. "He's doing one aspect of it well, but the other aspect must not be forgotten."

The Islamist militants, who operate chiefly in Nigeria's restive north, have carried out numerous deadly attacks on mosques, churches and businesses and are suspected of having links to al Qaeda.

Obasanjo said he had tried to reach out to Boko Haram about a year and a half ago through a lawyer who was acting as the group's proxy, and had asked if they had external backing.

The lawyer told him that the group was receiving support from other Nigerians who have resources overseas or "other organizations from abroad," Obasanjo said.

"If they had 25% support a year and a half ago, today that support has doubled," the former president said.

Analysts suggest that reaching out to Boko Haram may be increasingly difficult because the group has split into different factions, some with a domestic focus and others with a more pan-jihadi approach.

Resolving the issue is key to Nigeria's progress, according to Obasanjo, who now heads an eponymous foundation that is working to promote human security across Africa.

"Boko Haram undermines security, and anything that undermines security undermines development, undermines education, undermines health, undermines agriculture and food and nutrition security," he said.

International rights group Human Rights Watch says Boko Haram has killed more than 2,800 people.

In a report published late last year, Amnesty International condemned the increasingly brutal attacks carried out by Boko Haram since 2009, but said Nigeria's security forces "have perpetrated serious human rights violations" in response. A military spokesman rejected the allegations.

The militant group, whose name means "Western education is forbidden," is fighting to impose a strict version of Sharia law in the northern part of the country.

In the past, the group attacked other Muslims it felt were on an immoral path, but it has increasingly killed Christians.

The U.S. State Department has accused Boko Haram of attacking mosques and churches to incite tensions between the two religious groups, hoping to drive a wedge between them. It has condemned some of the group's leaders for alleged ties to al Qaeda.

Nigeria has almost equal numbers of Christian and Muslims, with the south predominantly Christian. Boko Haram and other Muslim groups say the north has been starved of resources and marginalized by the government of Jonathan, a Christian.

However, despite the ongoing challenges the country faces, Obasanjo said he does not foresee Nigeria ever splitting in two, into north and south.

"We in Nigeria now know that it would cost us much more to break up than it will cost us to come together," he said.

CNN's Zain Verjee, Laura Smith-Spark and Clare Garnett reported from London, and David McKenzie from Johannesburg.