Top Nabors shareholder says "increasingly concerned"

Jan 23 (Reuters) - Pamplona Capital Management, holder of 9.3 percent of Nabors Industries Ltd, has become "increasingly concerned" over the underperformance of the drilling rig contractor's shares, according to a filing on Wednesday.

Pamplona, a fund backed by Russian billion?aire Mikhail Fridman's Alfa Group, also said in the filing with the U.S. Securities and Exchange Commission that it had "valuable insights" to contribute to the development of Nabors' business, and that it has had constructive discussions with its management.

Pamplona was reporting an 8.8 percent stake held by the fund in addition to another 0.5 percent of Nabors owned by its founder, Alex Knaster.