Melanne Verveer, US ambassador-at-large for global women's issues, told a House of Representatives subcommittee that despite comprising half the world's population, women hold fewer than one-fifth of positions in national governments.

"All too often, important decisions that affect women, their families and their societies are made without their ever having a voice," Verveer said.

Verveer said women have made inroads at the local level, particularly in India, where they are about 40 percent of all elected representatives in villages and municipal councils. She also noted successes in Kuwait, where four women were elected to Parliament last year, a first in the Arab country. Women in Kuwait have had the right to vote and run for office since 2005.

Quotas within Iraq and Afghanistan's constitutions have helped pave the way for female politicians in those violent countries, Verveer said. But the gains are fragile, she said, as women face threats and have to put their lives on the line to visit their constituents.

The political improvements have to be nurtured "or women will risk seeing them erased or eroded," she said.

Women won Senate nominations in four states in Tuesday's primary elections in 12 US states, outright nominations for governor in two states, and a commanding edge for a gubernatorial nomination in a third state.

Democratic Rep. Lynn Woosley said women still have a way to go in the United States, where they hold about one-sixth of the seats in the House and the Senate.

Rep. Dana Rohrabacher, a Republican, noted the progress that women made in his state, California, with Meg Whitman and Carly Fiorina winning the Republican nominations for governor and Senate. California's two senators are women, both Democrats; Sen. Barbara Boxer was renominated in the Democratic primary Tuesday.

"I don't think that would have happened 20 years ago," Rohrabacher said.