The move followed what sources said were the weekend resignations of two top Yemeni officials to protest a government crackdown on protesters that left 52 people dead last week.

Yemen's chief prosecutor has launched an investigation into the shootings at Sanaa on March 18 and is questioning 17 suspects accused of orchestrating the massacre.

News of Human Rights Minister Huda al-Bann's resignation came from an official in her office who is not authorized to speak to the media and asked not to be named.

The resignations came amid new signs of cracks in support for President Saleh.

Tens of thousands of people protested outside Sanaa University in the capital on March 20, eyewitnesses said.

Funerals were held on March 20 for some of the people killed in attacks two days earlier, with bodies of the victims carried through the streets.

In addition to the fatalities, more than 100 people were hurt on March 18 in clashes between tens of thousands of anti-government protesters and security forces outside the university.

President Saleh announced that a state of emergency had been declared, and he expressed his “deep regret” over the casualties.

Mr Saleh said he would not run for another term in the next round of elections. He also has pledged to bring a new constitution to a vote by the end of the year and transfer government power to an elected parliamentary system.