Republican presidential hopeful Ted Cruz is expected to win most of the 14 delegates up for grabs in Wyoming, beating rival Donald Trump, who made little effort to win the rural state, and further narrowing the race for the party's nomination.

Mr Cruz is trying to prevent Mr Trump from obtaining the 1237 delegates needed to secure the Republican nomination at the July convention in Cleveland.

By continuing to rack up small wins, Mr Cruz is gaining ground on the New York real estate mogul, who has thus far failed to shift his focus on the local-level campaigning necessary to win delegates.

While Mr Trump has won 21 state nominating contests to Mr Cruz's nine, the billionaire leads the Texas senator by only 208 delegates (755-545). That means he must win nearly 60 per cent of those remaining before July.

Wyoming does not hold a primary vote. Instead, 475 party activists convened in Casper on Saturday to hold a state convention and award 14 delegates.  Previously, 12 other delegates had been designated at county-level conventions. Mr Cruz won 10 of those, with one going to Mr Trump and another being elected as "unbound.

Mr Cruz spoke at the convention, capping off a month-long effort to organise support in the state.  He spoke about local issues in Wyoming, the largest coal-producing state. He discussed the Democratic "attack" on the fossil fuel, saying President Barack Obama has tried to put the coal industry out of business through government regulations targeting air pollution.

"America is the Saudi Arabia of coal, and we are going to develop our industry," he said.

Mr Trump had originally planned to send former Alaska Governor Sarah Palin, who remains popular among conservatives, as a surrogate, but she cancelled at the last minute.