Republican Mitt Romney won primary votes in the southern states of Alabama and Kentucky, bringing him within arm's reach of scoring the delegates needed for his party's formal White House nomination.
The Republican nomination race has been largely academic for months since the other main candidates have dropped out, and Romney is the party's nominee in all but name.
In Arkansas, Romney had around 71 percent of the vote against 14 percent for his nearest rival, Rick Santorum, who has already dropped out of the race, according to data from the Arkansas secretary of state with four percent of precincts reporting.
And in Kentucky, Romney won around 67 percent of the vote against 12 percent for his nearest rival, Ron Paul, the Kentucky state board of elections said with nearly all precincts reporting.
A total of 75 delegates were at stake in the primaries.
Romney is likely to reach the magic number of 1,144 delegates to formally clinch the party nomination when Texas voters cast primary ballots on May 29.
For weeks, Romney has been in a general campaign mode, raising money nationally and attacking President Barack Obama, a Democrat who is seeking a second White House term in the November 6 general election.
The Republicans formally nominate their presidential candidate at the party's convention in August in Tampa, Florida.