(Reuters) -U.S. Senators Ron Wyden and Elizabeth Warren wrote a letter to UnitedHealth executives asking for information about the loans the healthcare conglomerate provided after the cyberattack at its tech unit last year.

In a letter to UnitedHealth CEO Stephen Hemsley and the group's industrial bank Optum Financial's chief executive, Dhivya Suryadevara, senators expressed concern over reports that the company used aggressive tactics to demand immediate loan repayments from healthcare providers, including threats to withhold payment for doctors' health insurance claims, if they do not pay in full immediately.

The cyberattack at Change Healthcare - the largest healthcare data breach in the United States to date - caused widespread disruptions in claims processing and impacted patients and providers across the country.

UnitedHealth loaned out more than $9 billion to providers who had been struggling after the massive ransomware attack in February last year.

"Now, more than 15 months after systems restoration and 14 months after the federal government ended its own assistance program, we have worked collaboratively with thousands of providers across the country to help them satisfy the repayment responsibilities they agreed to when accepting funds," Change Healthcare said in an emailed statement on Thursday, adding that it remains open to "reasonable repayment arrangements."

In the letter, dated Wednesday, the Democratic senators asked for data indicating the total number of loans provided, the criteria used to issue loans, copies of repayment plans, among others.

The company is expected to respond to the queries no later than September 12.