UPDATE: 4:40 a.m. EST -- Tunisian security officials said Wednesday that the attack on a presidential guard bus Tuesday was carried out by a suicide bomber, Reuters reported.

No group claimed responsibility for the blast that killed at least 12 people and forced the government to declare a nationwide emergency.

Original story:

United Nations Secretary General Ban Ki-moon has condemned Tuesday's attacks on a bus carrying presidential guards in the Tunisian capital. An explosion on the bus killed at least 12 people and injured 20, prompting President Beji Caid Essebsi to announce a state of emergency and a nightly curfew starting 9 p.m. local time (3 p.m. EST).

“The Secretary-General reiterates that the United Nations will continue to stand with the people of Tunisia as they confront the scourge of terrorism and continue to consolidate and strengthen their democracy,” a statement read.

The U.N. Security Council also said, according to the Associated Press (AP), that "no terrorist attack can reverse the path of Tunisia towards democracy and its efforts towards economic recovery and development."

The Tunisian government described the blast along a tree-lined avenue in Tunis as a terror strike, for which no group claimed responsibility immediately. The country is currently struggling with Islamist extremist violence despite being the only Arab Spring country known to have established a strong new democracy.

Earlier this year, extremists staged two other attacks in the country killing 60 people, hurting the country’s tourism industry, the AP reported. In June, a gunman attacked a beach resort, killing 38 tourists, and earlier this year, another attack at a museum killed 21 people. Both the attacks were claimed by the Islamic State group. Tuesday's attack reportedly came just days after the country’s authorities increased the security level in the capital and deployed several security personnel.