"There are many questions yet to be answered about what caused this disaster, but I am confident that the answers provided by federal, state and local officials can offer lessons that will help avoid tragedies like this one in the future," U.S. Labor Secretary Thomas Perez said in a written statement.
One company official cast doubt on reports that an explosion caused the collapse and fire.
Kim Nguyen, the international marketing manager for the company, said an investigator told company officials there was no explosion, "only a collapse of the building." She said she could not recall the name of the investigator, and said the person did not know what caused the building to collapse.
Nguyen urged people to wait for investigators to complete their study before drawing conclusions.
"This is a nightmare to people here," Nguyen said. "It's just shocking to everyone right now. We work as a family."
Calls and emails to other company officials were not immediately returned Tuesday.
Besides the two deaths, 17 people were injured, including 10 workers who were sent to hospitals. Hospitals reported that four of the 10 had been released by Tuesday.
Monday's deaths were not the first workplace fatality to occur at the plant.
OSHA records show International Nutrition was assessed more than $13,000 in penalties for a 2002 accident that killed a 45-year-old worker. The worker died when he fell into a moving mixer that he was cleaning.
The plant also was cited for six safety violations in 2012, ranging from a lack of facilities to flush dangerous chemicals from workers' eyes and skin to concerns over lacking safeguards for some equipment.2nd body recovered from Omaha plant that collapsed