At least 12 Tunisian presidential guards were killed and several others were wounded in a suspected suicide bombing targeting their bus in Tunis Tuesday evening, interior ministry officials said.

The deadly blast explosion occurred at a bus stop in Mohammed V Avenue, where the security guards posted at the presidential palace were boarding the bus to be taken to the palace on the outskirts of the capital city, according to DW.

"I was working and I heard a loud explosion. Everyone began to panic. People were crying and screaming, not knowing what was happening. The security guards shut down the whole mall because they were worried about another attack," eyewitness Firas Jaouani told Middle East Eye.

President Beji Caid Essebsi has declared a nationwide state of emergency and has imposed a curfew in Tunis after the deadly bombing.

"As a result of this painful event, this great tragedy... I proclaim a state of emergency for 30 days under the terms of law and a curfew in greater Tunis from 9:00 pm (2000 GMT) until 5:00 am tomorrow," Essebsi said in a televised address, according to AFP.

"We will continue with this war with all the people and ammunition that we have. Victory will be on the side of Tunisia," he said, according to Aljazeera.

Tuesday's bombing is the third major terror attack in Tunisia this year. ISIS jihadists have targeted foreign tourists at the Bardo Musean in Tunis and at a beach resort in Sousse earlier this year.