The Corruption Eradication Commission (KPK) is intensifying its investigation into a graft case pertaining to coal-powered power plant (PLTU) construction in Riau.

KPK spokesman Febri Diansyah said investigators had searched the offices of state-owned electricity company PLN and its subsidiary, PT Pembangkitan Jawa Bali (PJB), in Jakarta.

"The search was conducted at the office of PJB's president director and other board of director members," Febri said on Monday.

Tempo.co reported the search was completed on Tuesday morning as investigators were seen exiting the building and carrying boxes and suitcases.

PLN president director Sofyan Basir confirmed the KPK had searched a number of rooms, including his office, at PLN headquarters.

"Every division room connected to the project was searched. I don't know what was taken," Sofyan said on Monday night.

The search was conducted after investigators raided his house in South Jakarta on Sunday, during which the KPK seized a number of documents related to the power plant construction.

"PJB has no role [in the project]. PLN and its subsidiary, God willing, are not involved in the case," Sofyan said.

Previously, the KPK named two suspects in the case, Golkar lawmaker Eni Saragih and businessman Johannes Budisutrisno Kotjo, for alleged bribery totaling at least Rp 4.8 billion (US$333,629) regarding the contract signing of cooperation for Riau-1 PLTU construction. (ahw)