"The secretary general intends to soon establish a panel of experts that will advise him on international standards and comparative experiences with accountability," Pascoe told reporters at the end of his three-day visit.
The UN estimates that at least 7,000 Tamil civilians perished in the final four months of fighting. Security forces wiped out the top Tamil Tiger leadership, ending 37 years of ethnic bloodshed on May 18 last year.
"I don't want to pre-empt and give you details of the panel's members or its broad mandate. They will be announced early next week," Pascoe said.
His remarks came despite objections from Colombo to Ban. Sri Lanka insists that government forces had not killed any civilians while battling Tiger rebels and hence there was no need for a probe.
Pascoe told Colombo that there should be accountability for the allegations of humanitarian and human rights violations. The UN says up to 100,000 people died in 37 years of fighting.
"Responsibility for carrying out a credible process that meets international standards rests first and foremost with the authorities of Sri Lanka," he said adding that the UN will closely follow Colombo's own reconciliation bid.
Sri Lanka has named a "lessons learnt" panel to study issues that led to conflict, but it has no mandate to investigate war crimes.
Pascoe said he was assured in talks with President Mahinda Rajapakse and other officials that the island's own reconciliation panel will be "credible" and "accountable".
"We will be interested in its progress," Pascoe said.
Japan's top visiting envoy Yasushi Akashi and US President Barack Obama's two senior advisers are also in Sri Lanka this week to press Colombo to ensure accountability for crimes against humanity.