At least 23 people have been killed by Yemeni pro-regime forces – including snipers – in a second day of clashes shaking the country’s capital, Sana’a, medical and security officials said.

Almost 50 people have died in the two days of fighting. It is the most serious outbreak of violence in months, as frustration again builds over the president’s refusal to step down after 33 years in power.

Thousands of protesters armed with sticks reportedly overran a camp belonging to the presidential guards in Sana’a.

Others were said to be headed toward the headquarters of the elite force led by President Ali Abdullah Saleh’s son Ahmed in the south of the city.

About 20 of those killed on Monday were on the central Hayel Street in the capital. They included a child and at least three soldiers who had defected to join the protesters.

Mortar shells thought to have been fired by pro-regime forces killed at least two other people in Sana’a, said officials speaking on condition of anonymity.

On Sunday, at least 26 people were killed when pro-regime snipers opened fire on tens of thousands of people who demonstrated in Sana’a to demand that Saleh step down.

Apart from those killed, scores of protesters suffered gunshot wounds and were taken to hospitals, according to Mohammed al-Maqtari, a doctor at a field hospital set up by the protesters.

The wounded included soldiers from Yemen’s 1st armoured division, which, along with its commander, joined the protesters more than six months ago.

Witnesses said the soldiers were involved in skirmishes with the presidential guards.

In the southern city of Taiz, at least one protester was killed and 15 others were wounded on Monday in clashes between anti-regime demonstrators and security forces, according to witnesses.

And in the southern port city of Aden, three protesters were wounded in clashes with government forces, witnesses there said.

Yemen’s protest movement has stepped up demonstrations in the past week.

The rebels have been angered after Saleh deputised the vice-president, Abed Rabbo Mansour Hadi, last week to negotiate further on a Gulf-mediated, US-backed deal under which the president would step down in return for immunity from prosecution.

Saleh has already backed away three times from signing the deal.

Many believe the move is the latest of many delaying tactics. Saleh has resisted calls to resign.

The US once saw Saleh as a key ally in the battle against a Yemen-based al-Qaida branch, which has taken over southern parts of the country under cover of the political turmoil.

The US withdrew its support of Saleh as the protests gained strength.