By Deena Beasley

April 25 (Reuters) - Amgen AMGN.O on Friday announced a $900 million expansion of its Ohio biotech manufacturing facility, becoming the latest in a string of drugmakers pledging to increase U.S. capacity amid Trump administration threats of potential import tariffs.

Amgen, based in Thousand Oaks, California, said the plans bring its total investment in central Ohio to more than $1.4 billion, creating 750 jobs.

Other drugmakers committing recently to U.S. manufacturing expansions include Eli Lilly, Novartis, Roche, and Johnson & Johnson.

Pharmaceutical Research and Manufacturers of America, the industry's trade group, has said it can take five to 10 years and $2 billion to launch a new U.S. production facility in part because of regulatory requirements. A study commissioned by the lobbying group found that tariffs could lead to higher drug prices.

U.S. President Donald Trump's administration has opened a national security investigation into pharmaceuticals in a bid to demonstrate why the U.S. needs tariffs to boost domestic manufacturing. Rates and timing remain uncertain, but the industry has been lobbying for phased-in tariffs.

Amgen said that since passage of the Tax Cuts and Jobs Act of 2017 it has invested almost $5 billion in U.S. capital expenditures, generating additional downstream output to the U.S. economy of around $12 billion.

The biotechnology company announced in December plans to invest $1 billion to build a second drug substance manufacturing plant in Holly Springs, North Carolina. Amgen also has manufacturing facilities in Massachusetts, Rhode Island, California and Puerto Rico.

Outside of the United States, Amgen's manufacturing operations are in Ireland, the Netherlands and Singapore.

(Reporting By Deena Beasley; Editing by Hugh Lawson)

((deena.beasley@thomsonreuters.com; 213 955 6746; Reuters Messaging: deena.beasley.thomsonreuters.com@reuters.net))