Ban expressed concern over killings in the violence hit country. Martin Nesirky, UN spokesperson, said that Ban spoke with Ouattara by phone yesterday in which the Ivorian leader said he had launched an investigation.
"The Secretary-General said those responsible should be held accountable," Nesirky said.
"President Ouattara, while denying his forces were involved, said he had launched an investigation and would welcome an international inquiry into the matter," he added.
The International Red Cross say about 800 people were killed in an operation by pro-Ouattara forces in the town last Tuesday as they took territory from Ivory Coast strongman Laurent Gbagbo.
Following a disputed election in November, incumbent leader Gbagbo and his rival Ouattara have been fighting to take power in the country.
The country`s election commission and a UN team have recognised that Ouattara as the winner of the elections.
This week, the Security Council imposed sanctions on Gbagbo.
India also raised objections to the UN siding with Ouattara and that its 10,000 strong peacekeeping force (UNOCI) should not be part of the political stalemate in the country.
"They (peacekeepers) cannot be made instruments of regime change," India`s envoy Hardeep Singh Puri said.
"The UNOCI should also not get involved in a civil war but carry out its mandate with impartiality and ensuring safety and security of peacekeepers and civilians."
On this point, China took a similar stand as India.
"China always believes that the UN peacekeeping operation should strictly abide by the principle of neutrality," said Li Baodong, the Chinese envoy, noting that UNOCI should avoid becoming a party to the conflict.