KAMPALA, Uganda — Rival security forces clashed in Sudan on Tuesday as huge crowds of protesters kept up their vigil outside army headquarters to call for the overthrow of the country’s longtime authoritarian president, Omar Hassan al-Bashir.

Seven people were killed on Tuesday, said Sara Abdelgalil, a spokeswoman for the Sudanese Professionals Association, which is organizing the protests.

The eruption of violence between different armed government forces is a major development in the four-month long protest movement against the president, said Magdi el-Gizouli, a fellow at the Rift Valley Institute, a think tank based in Kenya.

“In a way, it has been turned into an internal dilemma between security forces,” said Mr. el-Gizouli, who is Sudanese.