WASHINGTON (Reuters) - Expanding on her gun control proposals, U.S. Senator Kamala Harris will announce on Wednesday that if elected president she will prohibit imports of some high-powered guns into the United States.

U.S. Democratic presidential candidate Kamala Harris participates in the She the People Presidential Forum in Houston, Texas, U.S. April 24, 2019. REUTERS/Loren Elliott

Harris has already endorsed a swath of gun control measures, but at a campaign stop in New Hampshire, she will promise to institute a ban on “AR-15-style assault weapons,” a senior campaign official said.

There is legal precedent for such a ban, the aide said, pointing to similar measures by former presidents Bill Clinton and George W. Bush taken in order to study permanent bans.

Harris is vying against more than 20 Democrats for the party’s nomination to challenge Republican President Donald Trump in the 2020 election.

The AR-15, or assault weapons, are catch-all terms often used by critics to describe semi-automatic rifles and other high-capacity fire arms.

Such guns were used in several recent mass shootings in the United States, but Congress has so far failed to ban them.

It is unclear just how many weapons Harris’ proposal would affect. Her campaign estimates 4 million rifles have been imported into the United States, based on industry figures.

The United States has a robust domestic market and 2.5 million rifles were made in 2017 alone, the most recent year for which the Bureau of Alcohol, Tobacco and Firearms provided data.

The figures did not distinguish between rifle types. About 159,000 of those made in the United States that year were exported.

Sturm, Ruger & Co., Inc., the largest domestic producer of rifles, including one similar to the AR-15, made about 253,000 in 2017 in Mayodan, North Carolina and 406,000 more in Newport, New Hampshire.

The campaign pointed to three foreign-based gun makers - Glock, Sig Sauer and Beretta. Glock, which makes a pistol used in several recent shootings, made more than 175,000 pistols in the United States in 2017.

Sig Sauer, which was spun off into a separate American company in the 1980s, made about 36,000 rifles in the United States in 2017. Beretta, which also has an American subsidiary, made about 2,700 rifles in the U.S. that year.

In Harris’ previous announcement backing gun control, she proposed giving Congress 100 days to pass legislation such as a universal background checks bill or a renewal of the ban on assault weapons, before using presidential executive power to act on the issue.

Harris said she would use executive power to require sellers of five or more weapons a year to run background checks for all gun sales; revoke the license of gun makers and dealers who break the law; reverse a move by Trump to redefine the term “fugitive from justice” that allowed gun purchases by people with outstanding arrest warrants; and close the boyfriend loophole.

An assault weapons ban adopted in 1994 during Bill Clinton’s presidency was among the reasons cited when Democrats lost congressional seats in that year’s midterm elections. The ban expired in 2004.