Attorney-general Mohamed Apandi Ali has returned the investigation papers on Penang Chief Minister Lim Guan Eng's bungalow purchase for further investigation.

"After studying all the explanations in the said investigation papers, this department finds there are several actions that need to be investigated further to complete this case.

"Therefore, the department today returned the investigation papers to enable the Malaysian Anti-Corruption Commission (MACC) to complete its investigations," Apandi said in a statement today.

He said the department hopes the MACC can return the completed papers promptly.

MACC earlier said its investigation into the purchase of Lim's bungalow at Jalan Pinhorn, Penang had been completed and handed its papers to the AG's Chambers on May 25 for follow-up.

Lim has been accused of acquiring the property for considerations below market price, allegedly in exchange for the approval of the sale of government land to Kuala Lumpur International Dental Centre (KLIDC).

The allegations were raised by Umno MP Shabudin Yahya in Parliament in March.

The chief minister had been renting the premises prior to the purchase, and has denied any wrongdoing and in March said he welcomed the MACC to probe him.

Lim added that the allegations had been raised before by Umno Bagan division chief Shaik Hussein Mydin, who in August 2015 had apologised to him before the court following legal action.