Sudan’s president, Omar al-Bashir, has appointed a new prime minister, but left the country’s current defence, foreign and justice ministers in place following the declaration of a one-year state of emergency.

Just hours after announcing that he would dissolve the country’s central and state governments, Bashir appointed new state governors who were all from the military, according to a presidency statement.

Bashir, who seized power in a 1989 coup, said on Friday he would postpone pushing for constitutional amendments that would allow him to seek a third term in office.

Facing genocide charges, Bashir’s rule has been rocked by civil wars and increasing street demonstrations. A heavy security crackdown has left scores of protesters dead. At least 57 people have been killed since December.

“Our country is passing through a difficult and complicated phase in our national history,” Bashir said in a speech televised live from the presidential palace in Khartoum. “We will get out of it stronger and more united and determined.”

In a rare acknowledgment, Bashir described the demands of the protesters as “legitimate” but said there were attempts to exploit the youth protests “to take the country to the unknown”.

The state of emergency will give the security forces a free hand in cracking down on protesters and carrying out detentions and it places heavier restrictions on the press and opposition parties.

The announcements were instantly met with street demonstrations, demanding Bashir step down. Witnesses said riot police fired teargas and arrested a number of protesters.

Sudan has been gripped by nationwide protests since 19 December. The demonstrations, which show no sign of abating, were triggered by rising prices and shortages but quickly turned to calls for Bashir to step down.

Bashir’s term ends in 2020 and he has repeatedly promised not to make new runs for the presidency. Without amending the constitution, he cannot run for a third term. His announcement came days after a parliamentary committee that is amending the constitution to scrap presidential term limits cancelled its meetings.

The Sudanese Professional Association, which is spearheading the country’s demonstrations, warned of any measures that could “turn against” the demands of the Sudanese people and vowed that it would respond with escalating street protests.

“The demands of this revolution are crystal clear,” the statement said. “The regime and its head must step down.”

However, Bashir warned the opposition of the “zero sum” game that created chaos, pointing to the wave of the Arab spring uprisings that led to civil wars in countries such as Libya and Yemen.

As he was speaking in the presidential palace, dozens of protesters were taking to the streets in Khartoum and other places, chanting, “just fall”.

Shelving intentions to amend the constitution to pave the way for a third term in office appears to be the only political concession Bashir has made so far after two months of demonstrations.

“What Bashir presented are tactics to keep his regime alive,” said Mubarak al-Mahdi of the Umma party. “Declaring a state of emergency means suppressing freedom of expression and demonstration and tightening grip on the revolution.”

Sudan’s main opposition groups called for a four-year transitional government followed by elections.