Myanmar leader Aung San Suu Kyi's party has won nearly half of the seats contested in by-elections, the first vote since it swept to power a year ago, but has been bruised by losses in ethnic minority areas.

Aung San Suu Kyi's National League for Democracy (NLD) won nine out of 19 seats in the national and regional parliaments on Sunday, according to the Union Election Commission, following a period in which she has struggled to match sky-high expectations.

The party faced losses in more remote areas, including in ethnic minority regions where ethnic violence has continued despite Aung San Suu Kyi's promise to bring peace after decades of strife.

An embarrassing defeat was in the southern state of Mon, where the NLD lost a lower house seat to its main opposition, the military-backed Union Solidarity and Development Party (USDP).

In a televised address earlier this week, Aung San Suu Kyi acknowledged the public's frustration with the slow pace of reforms and development in the country.

However, she also reiterated her top priority of ending the ethnic conflicts that have kept Myanmar in a state of near-perpetual civil war.

While the outcome of the by-elections will not affect the balance of power within the parliament, where the NLD enjoys a large majority, it offers a chance to gauge the popularity of the administration in a country where nationwide public polls are not available.

Language barrier

Win Htein, one of the NLD's top leaders, said the party faced language barriers and problems with armed groups in the Shan state districts being contested. Fighting in some of those areas has intensified in recent months.

"We are still improving in Shan state. The local people don't understand Burmese, so we have to translate our policies into the Shan language," he said.

Major rebel armies engaged in clashes with the military in areas including the Shan state have refused to actively participate in Aung San Suu Kyi's peace process.

Several conflicts have reignited since Aung San Suu Kyi took office, displacing an estimated 160,000 more people, according to the United Nations.

Over two million voters, less than five percent of the country's population, could vote in the by-elections where seats in eight states and regions across the country were up for grabs.

Nobel Peace Prize winner Aung San Suu Kyi is also facing international criticism for her government's handling of a crisis in the Muslim-majority Rakhine region, where soldiers have blocked access for aid workers and are accused of raping and killing civilians.