Afghan officials say a suicide bomber has killed a cousin of President Hamid Karzai in the southern province of Kandahar.
In a written statement, the president said his family is not immune to the violence other Afghanis experience every day.
Just like all other Afghans who are the daily targets of terrorist attacks, our family too is no exception and as every other Afghan, we too will have to bear it," said Hamid Karzai.
No one has claimed responsibility for the bombing.
Hashmat Karzai was seen as a powerbroker in Kandahar and led the election campaign of presidential candidate Ashraf Ghani, one of two hopefuls vying to replace Karzai.
Ghani wrote on Twitter that his adviser's death should bring Afghans together against their common enemies.
"We'll not succumb to coward acts of the enemies of [Afghanistan]. Every loss of Afghans reminds us that [we] must stay united to overcome the challenges," said Ghani.
Graeme Smith, an Afghanistan researcher at International Crisis Group, told VOA Afghan radio that the attack has the markings of Taliban-organized assassinations targeting key figures in the region.
"Anybody who can be helpful to the governing of a dangerous and unruly place like Kandahar becomes a target," said Smith.
Hashmat Karzai led the election campaign of presidential candidate Ashraf Ghani, one of two hopefuls vying to replace Karzai.
Ghani wrote on Twitter that his adviser's death should bring Afghans together against their common enemies.
"We'll not succumb to coward acts of the enemies of [Afghanistan]. Every loss of Afghans reminds us that [we] must stay united to overcome the challenges," Ghani said.
Graeme Smith, an Afghanistan researcher at International Crisis Group, tells VOA Afghan radio that the Taliban may be behind the killing of Hashmat Karzai, in an effort to undermine the government.
In a statement, the U.S. Embassy called for the attack's perpetrators to be brought to justice.
It's not the first time the president's family has been the target of violence.
In 2011, Hamid Karzai's half-brother Ahmad Wali Karzai, who headed a provincial council, was killed by a bodyguard at home.
Tuesday's attack comes amid heightened tensions in the country, as Ghani and his opponent Abdullah Abdullah dispute a June 14 presidential runoff vote.
Preliminary results put Ghani ahead but Abdullah rejected the outcome and alleged massive fraud.
In a deal mediated by U.S. Secretary of State John Kerry, the rival presidential candidates agreed to a full U.N.-supervised audit of the entire runoff poll and committed to abide by the final results.
VOA's Afghan Service contributed to this report.
