Zalmay Khalilzad said he was “relieved” that Fawzia Koofi had escaped Friday’s shooting “without serious injury”.
Ms Koofi was shot in the right arm while travelling with her sister.
The Taliban have denied they were behind the attack, which came as the two sides prepared for talks.
The militant group has previously refused to negotiate directly with the Afghan government, but agreed to take part in the talks aiming to end almost two decades of conflict after reaching an agreement with the US in February.
As part of the agreement, the Afghan government had to release 5,000 Taliban prisoners. On Thursday, it began releasing the last 400 militants. Talks are expected to start in Qatar after the final prisoner is released.
But there are concerns the attack on Ms Koofi, an outspoken critic of the Taliban who was returning from a meeting in the northern Parwan province when she was attacked near the capital Kabul, could undermine the process.
“Worrying pattern of targeted attacks that can negatively impact confidence in peace process,” the chief of Afghanistan’s Independent Human Rights Commission, Shaharzad Akbar, wrote on Twitter.
Mr Khalizad also took to Twitter, saying he wanted “all sides who seek peace to not only condemn the attack but to accelerate the peace process and start intra-Afghan negotiations ASAP”.
Media captionIs peace with the Taliban possible?
The attack, which no one has claimed, was also condemned as “cowardly” by President Ashraf Ghani and Abdullah Abdullah, the head of the High Council for National Reconciliation.
Ms Koofi is one of the few women to have taken part in dialogue with the hard-line Islamist group, which ruled Afghanistan until they were removed from power in Afghanistan by a US-led invasion in 2001.
They have fought to regain territory since. Last year alone, more than 3,000 civilians were killed in the conflict, according to United Nations figures.
However, the deal reached with the US has proved controversial. On Saturday, France objected to the release of some of the remaining 400 prisoners held by the Afghan authorities – some of whom it says were involved in the killings of French nationals.