Lesotho's embattled Prime Minister Thomas Thabane said on Monday he is stepping down, ending months of political uncertainty gripping the kingdom since he was accused of having a role in his ex-wife's murder.

"I decided to personally come and inform you that I am stepping down as prime minister of Lesotho," he told supporters in his Abia home constituency on the outskirts of the capital Maseru.

Lesotho has been plagued by political instability since the start of this year after police accused Thabane of having a hand in the killing of his estranged wife in June 2017.

Thabane and his then wife Lipolelo Thabane, 58, were in the midst of a bitter divorce when she was shot and killed outside her home two days before her husband's 2017 inauguration.

Thabane has denied involvement in the murder and had been under mounting pressure to resign.