WASHINGTON (Reuters) - Major US long-term care insurers, including Genworth Financial and Manulife Financial, are being asked about "troubling data" showing a sharp jump for the industry in claims-related complaints, a senior Republican lawmaker said this week.

Iowa Senator Charles Grassley sent letters last week to US insurance providers "to learn more about how effectively the sector is meeting the needs of Americans who have purchased such policies," he said.

Grassley, the top Republican on the Senate Finance Committee, said he made the request after learning about industry trends from the National Association of Insurance Commissioners.

The group reported a 92 percent jump in long-term care complaints nationally from 2001 to 2006 and "a steady increase in the number of complaints regarding claim denials," he said.

It also identified a 74 percent increase in claim denial related complaints between 2003 and 2006.

"While this may be explained by the increasing number of people purchasing long-term care insurance, the relationship remains unclear," Grassley said in the letter, which also went to Conseco Inc, MetLife Inc, Penn Treaty American Corp, Unum Group, Prudential Financial Inc and others.

The Senate Finance Committee oversees the federal government's Medicare and Medicaid health care programs.

Grassley said in his letter that any increase in rejected long-term care insurance claims could place "a substantial and perhaps unnecessary financial burden ... on Medicaid."

Grassley asked congressional investigators in April to examine the industry after press reports of problems.