SAN'A, Yemen - Tens of thousands demonstrated Sunday in Yemen's capital against the deaths of protesters and demanded the resignation of the vice president for failing to bring the killers to justice.

Marching past the office of Vice President Abed Rabbo Mansour Hadi, the protesters denounced him as a "tool in the hands" of outgoing President Ali Abdullah Saleh.

The march took place as Hadi was meeting with U.S. Ambassador Gerald Feierstein. A statement from Hadi's office said they discussed Yemen's crisis, and Hadi appealed for calm.

Hadi is heading a transitional government after Saleh agreed to transfer power after months of demonstrations and turmoil. Under the U.S.-backed plan, Saleh won immunity from prosecution, angering many of his opponents. Yielding to pressure to defuse the country's tensions, Saleh said Saturday that he would leave for the United States.

The United States is concerned about months of turmoil in Yemen that has led to a security breakdown because the dangerous al-Qaeda branch in the country has taken advantage of the vacuum to expand its presence in Yemen's south.

A security official said al-Qaeda-linked forces Sunday killed an intelligence chief responsible for fighting terrorism in southern Yemen. Col. Hussein el-Shabibi was shot dead by masked gunmen while in his car in a market in Sheik Othman, Aden, the official said.

In the capital, San'a, troops commanded by Saleh's relatives attacked protesters Saturday, activists said, killing at least nine and setting off Sunday's demonstration. They said the elite Republican Guard troops led by Saleh's son Ahmed fired at protesters, and dozens were arrested by the national security police led by Saleh's nephew.

"The situation will not stabilize, since Saleh's relatives and supporters are still holding sensitive positions in the army and government," said Fathi al-Rawdi, an activist at Sunday's gathering.

Activist Ahmed Ghilan criticized the power-transfer deal Saleh signed in November.

"We are fed up with this tragic farce deal that gives immunity but is impotent to force Saleh's troops out of the main streets," Ghilan said.

A military committee formed by the vice president was assigned to arrange the withdrawal of all army units and armed groups from the streets. That was supposed to be completed Saturday.