The Sambisa Forest in northeast Nigeria is Boko Haram's final stronghold in the country.
People are waiting for hours to get gas in the West African country.
The trials of a pro-Buhari lobby group have sparked a social media storm.
Shekau has not been heard from since March 2015.
The former Niger Delta kingpin has been on the run since January.
Other African leaders have also condemned the attacks, which killed at least 30 people.
The NNPC previously denied it failed to submit funds to the public purse.
At least 300 people died in clashes between the Nigerian Army and the country's main Shiite movement.
At least four people were killed during an election rerun in the oil-producing state.
The militant group launched its first attacks in 2009 in Maiduguri.
President Muhammadu Buhari has vowed to tackle "mind-boggling" levels of corruption in the oil industry.
President Buhari's party said its members are an "endangered species" in the oil-producing state.
Ex-Nigerian ruler Sani Abacha is suspected to have looted up to $5 billion in public funds during his reign.
The pro-Biafra activist is on trial for treasonable felony and faces a maximum life sentence.
Two of Nigeria's four state-run refineries remain closed due to attacks on oil pipelines.
Nnamdi Kanu, the pro-Biafra leader, goes on trial for treasonable felony in Nigeria on Monday.
James Ocholi, who was appointed in November 2015, died with his wife and son.
Uchechi Okwu-Kanu says she almost miscarried during her husband's detention.
The country's budget was announced in December, but several issues have stalled its implementation.
Angela Rayner says that allegations of human rights abuses against pro-Biafra protesters in Nigeria require investigation.
A revived secessionist movement is adding to Nigeria's troubles.
The Nigerian Shiite leader was arrested in December 2015 and is being held without charge.