WASHINGTON — Former Massachusetts Gov. Mitt Romney added to his big lead in the race for convention delegates Tuesday by sweeping Republican presidential primaries in North Carolina, Indiana and West Virginia, inching closer to the number of delegates needed to clinch the GOP nomination.

Romney won at least 60 delegates Tuesday, with 35 still undecided. Romney has a commanding lead in the race for delegates with 916. He is 228 delegates shy of the 1,144 he needs to clinch the nomination — a gap he could close by the end of the month.

The only other Republican still in the race, Texas Rep. Ron Paul, has 99 delegates. Paul won at least five delegates Tuesday, all in North Carolina

Romney won all 27 delegates at stake in Indiana and at least 33 of the 52 delegates up for grabs in North Carolina. Voters also went to the polls in West Virginia, with 28 delegates at stake, but delegate results were not expected on election night.

West Virginia elects individual delegates directly on the ballot. Each delegate is listed on the ballot — three in each of the three congressional districts and 19 statewide — along with the presidential candidate they support. With 112 candidates running for the 19 statewide spots, results were expected to be late.

North Carolina awarded delegates in direct proportion to the statewide vote, and Rick Santorum and Newt Gingrich were on the ballot even though both have dropped out of the race. Santorum won at least four delegates and Gingrich won at least three.