US ambassador Robert Blake gave a list of 355 names of people whose whereabouts were unknown, the foreign ministry said.
It said Colombo took the issue seriously and had launched investigations into the list presented soon after a visit here in March by US Assistant Secretary of State Stephen Mann.
Mann raised concerns about human rights during his visit.
The Colombo government's statement came amid mounting local and international criticism of the island's rights record.
The US list of names contained a number of repetitions, the foreign ministry said in a statement.
It did not say when the victims had disappeared or been abducted.
The US embassy confirmed that the United States had supplied Colombo with the list but declined to discuss details.
The statement came a day after a presidential commission said 430 civilians, were reported killed between September 14 and February 25 as the tropical island's Tamil separatist conflict escalated.
The majority of the d