Malaysian helicopter operator Weststar Aviation Services, partly owned by U.S. private equity company KKR, is inviting banks to pitch for a share listing slated for 2015, sources said.

The initial public offering (IPO) could raise between $300 million to $600 million, the sources said, and comes a year after KKR bought a stake in the company, the private equity firm's first asset in Malaysia.

Weststar, controlled by Malaysian tycoon Syed Azman Syed Ibrahim, is the largest provider of chartered helicopters to oil and gas companies in Southeast Asia with a fleet of 45 helicopters.

The company has previously said it was looking to list in the first quarter of next year after KKR bought a "substantial minority" stake in the company for 642 million ringgit.

The banks are due to submit their proposals by the end of the first week of October, according to the sources, who declined to be named as they are not authorised to speak to the media.

Weststar officials were not immediately available for comment.