The Nigerian politicians involved have denied the allegations.
At least four villagers were killed in the attack Tuesday.
Scores of people were reportedly killed in the clashes, but the army says the claims are "calumny."
A senior doctor said the president's decision flies in the face of a promise to end medical tourism.
The Niger Delta Avengers group has slashed Nigeria's oil production by 600,000 barrels per day.
Nigeria has recovered more than $500 million in cash and has seized over $9 billion in assets.
Some Nigerians are wondering why he doesn't receive treatment at home.
The Nigerian army says six people were killed in a separate attack in the Niger Delta.
The oil-producing region has been the site of multiple attacks by a militant group in recent months.
Militants including the Niger Delta Avengers have carried out attacks on oil pipelines, cutting production.
Two Emirs return to Borno State to celebratory crowds after being forced to flee by radical Islamists.
Minister of Foreign Affairs, Geoffrey Onyeama, says the pact is expected to cause an upsurge in economic activities.
Boko Haram militants abducted 276 girls from their school in Chibok more than two years ago.
Trade unions are angry about a 66 percent increase in fuel prices.
Petrol prices will increase by two-thirds, but the government hopes it will resolve a severe fuel shortage.
Much of Boko Haram's success has been down to the misappropriation of billions of dollars of Nigerian funds.
A new militant group called the Niger Delta Avengers have been attacking oil pipelines in recent weeks.
The British prime minister referred to Nigeria as "fantastically corrupt."
David Cameron referred to Nigeria and Afghanistan as "possibly the two most corrupt countries."
The comments are likely to make the visit of Nigeria and Afghanistan's presidents on Thursday rather awkward.
More than 1 million people died in Nigeria's war with Biafra.
Kanu's defense wants to overturn a ruling that allows witnesses to testify anonymously.