(Reuters) - Paramount Global has begun the second phase of its planned layoffs in the United States as the media giant pushes toward increasing profitability, according to an internal memo seen by Reuters.

The cuts are part of the company's efforts to reduce annual costs by $500 million as it looks to streamline its operations ahead of its merger with Skydance Media.

Paramount began cutting jobs in August, and plans to lay off 15% of its U.S.-based workforce in three phases by the end of the year. About 90% of the layoffs will be complete after Tuesday, the memo said.

The firm also wrote down the value of its cable networks by $6 billion last month as it grapples with a decline in its traditional cable television business, driven in part by advertisers increasingly shifting their spending to streaming platforms.

The job cuts are expected to lead to charges of $300 million to $400 million in the third quarter, company executives had said in August.

(This story has been corrected to clarify that the company 'plans to lay off 15% of U.S.-based workforce in three phases by end of year,' not 'began cutting jobs in August, starting with 15% of its workforce,' in paragraph 3)

(Reporting by Zaheer Kachwala in Bengaluru; Editing by Tasim Zahid)