Yemen's former prime minister has rejected his sacking by the president, calling the move a "coup" and an affront to the constitution.

In a statement late Tuesday, Khaled Bahah, who was also vice president until President Abed Rabbo Mansour Hadi's decision last weekend, said the move undermined state authority.

Hadi fired Bahah over what he called shortcomings in the government's performance and appointed a successor while naming Bahah a presidential adviser.

Yemen, the Arab world's poorest nation, has been torn by conflict since 2014, when Shiite rebels known as Houthis and allied with a former president captured large swaths of the country, including the capital, Sanaa.

In March 2015, a Saudi-led military coalition launched airstrikes against the Houthis and later, a ground operation to retake back ground from the rebels.