The blast occurred at 6.10 a.m. Moscow time (3.10 a.m. GMT) outside a conference hall, 300 meters (about 1,000 feet) from the palace. An international conference was to take place in the building later on Wednesday and Tajik Prime Minister Akil Akilov was due to attend the event.
"He [security guard] saw a plastic bag lying near a wall, he picked it up and the bag exploded in his hands," Kasym Gafarov, a senior security official told reporters. "The guard died instantly."
Dushanbe prosecutors opened a criminal investigation into the incident, which Tajik authorities consider a terrorist act.
"It is a terrorist act and the capital's prosecutors have launched an investigation under a corresponding article of the Criminal Code," Dushanbe prosecutor Kurbonali Mukhabbatov said.
Tajikistan, a former Soviet republic in Central Asia, is a major transit country for drugs from the world's largest heroin producer, Afghanistan, to Russia and some Western countries. Tajikistan's long-serving leader, Emomali Rakhmon, has repeatedly blamed Islamist militants for trying to destabilize the situation in the country.
Although Tajikistan boasts a strategic location, it has few natural resources besides hydroelectric power, cotton and aluminum. Foreign aid has been assisting the country's economy since 1997, when a devastating five-year civil war ended.
