The official is familiar with the spill oversight but would not clarify what is seeping near the well.
BP blocked the well Thursday afternoon by shutting valves on a new containment system to enable pressure tests.
But it remains unclear if the well will remain capped, or if the flow will resume to allow capture through an improved containment network that federal officials say has the capacity to handle all of the petroleum coming from the well.
The ultimate solution is a relief well BP is drilling that is expected to kill the leaking well for good next month.
National Incident Commander Adm. Thad Allen has suggested in recent days that the well is likely to be reopened. In a statement early Sunday afternoon, he said ongoing well integrity tests would continue until late in the afternoon, with the potential for additional extensions in 24-hour increments.
“As a condition of the extension, the U.S. government has required significant new monitoring and periodic evaluation and approval by our science team,” he said.
“Work must continue to better understand the lower than expected pressure readings. This work centers on two plausible scenarios, depletion of oil from the reservoir and potential leakage caused by damage to the well bore or casing,” Allen added.
Re-opening the well could allow oil to flow back into the Gulf unchecked for a period while the systems that funnel the oil to the surface are re-attached, according to BP, which has suggested the cap could remain closed.
“No one wants to see oil flowing back into the sea, and to initiate containment would require that to occur,” BP Chief Operating Officer Doug Suttles said Sunday, according to numerous press reports.