Romney sprints clear of rivals with three primary wins

Mitt Romney tightened his grip on the Republican presidential nomination, sweeping three primaries in Wisconsin, Maryland and Washington, DC, and urged his party to shift focus to the general election showdown with President Barack Obama.

The victories enabled Mr Romney to extend his already considerable delegate lead over chief Republican rival Rick Santorum, who flashed defiance in the face of growing pressure to abandon his own candidacy in the name of party unity.