A Maine Republican National Committee member and six state committee members have resigned and left the GOP, a sign of continued tensions within in the party as it attempts to unify ahead of the 2014 elections. Libertarian-leaning committee member Mark Willis of Washington County and the others resigned in a letter Sunday, citing concerns about the party’s direction in Maine and across the country. The letter was signed by six others Republicans, including former Senate candidate Scott D’Amboise and Sam Canders, who challenged Rick Bennett for state party chairman last month. All 13 said they are withdrawing from the party. The group pointed to a number of issues, including Maine GOP lawmakers’ failure to override Governor Paul LePage’s veto of the state budget, which raised the meals and lodging and sales taxes. It also criticized Republicans in Congress for backing ‘‘feel good,’’ restrictive, and ineffective gun control legislation.