Republican presidential hopeful Rick Santorum easily won the Kansas caucuses to consolidate his status as the main challenger to front-runner Mitt Romney and to dispel any lingering hopes of an early conclusion to the race.

The scale of his victory highlighted his hold on the party's conservative base, especially in the Midwest, and its lack of enthusiasm for Romney.

The victory boosts Santorum going into next Tuesday's contests in Mississippi and Alabama.

Romney had hoped the contest would be over by now but Santorum is stubbornly clinging on and, as long as he keeps picking up states such as Kansas, there is no incentive for him to quit. Santorum adds Kansas to wins in Iowa, Minnesota, Colorado, Tennessee, Oklahoma and North Dakota and is almost certain to take Missouri next Saturday.

With half the votes counted, the Associated Press called the result for Santorum.

As a small compensation for the loss of Kansas, Romney won three other Republican contests: the US Virgin Islands and two in the Pacific, Guam and the Northern Mariana Islands. They have a combined total of 21 delegates, all of which went to Romney. Kansas had 40 delegates at stake.

A candidate needs 1,144 delegates to the Republican convention in August to secure the party nomination to take on Barack Obama for the White House in November.

Romney has opened up a big delegate lead but is still far short of a winning total. According to the Associated Press, Romney has 441 delegates, including those from Guam, the Marianas and the Virgin Islands. Santorum had 183 before the Kansas delegates were awarded. Gingrich has 107 and Ron Paul 46.

Romney sent one of his sons, Matt, to Guam to campaign on his behalf. "I am grateful to have won all nine delegates in Guam, and I am pleased that my son Matt was able to visit the island on my behalf and be there for the caucuses," Romney said in one statement.

Neither Romney or Gingrich campaigned aggressively in Kansas, having concluded last week that Santorum was going to win. Gingrich cancelled planned campaign events in Kansas on Friday to concentrate instead on Mississippi and Alabama.

Santorum is hoping that Gingrich might pull out off the race if he fails to win Mississippi or Alabama, allowing him to head-to-head with Romney. Paul so far has failed to win a single state but said he intends staying in the race.