May 23 (Reuters) - Elon Musk's artificial intelligence startup, xAI, is seeking to raise close to $6 billion in a funding round backed by Silicon Valley heavyweights including Andreessen Horowitz, the Financial Times reported on Thursday.

The round would value the startup at $18 billion, and also includes commitments from Sequoia Capital and Tribe Capital, the report said, citing people familiar with the negotiations.

The AI race has been heating up, with several investors signing big checks for start-ups looking to compete with market leaders like OpenAI.

Representatives for Musk and the investment firms did not immediately respond to Reuters' requests for comment.

Musk had denied a report earlier this year that said xAI was seeking funding. (Reporting by Niket Nishant in Bengaluru; Editing by Maju Samuel)