US Secretary of State John Kerry condemned the "awful" car bombings blamed on pro-Damascus groups that killed at least 43 people in a Turkish town near the Syrian border on Saturday.
"The United States condemns today's car bombings and we stand with our ally, Turkey," Kerry said in a statement.
"This awful news strikes an especially personal note for all of us given how closely we work in partnership with Turkey, and how many times Turkey's been a vital interlocutor at the center of my work as secretary of state these last three months."
US Ambassador to Turkey Francis Ricciardone also strongly condemned also the "vicious attack," as Kerry offered his "deepest condolences" to the families of the victims and his thoughts with the wounded.
The bombings were the deadliest in Turkey, a key supporter of the Syrian opposition, since the conflict began more than two years ago.
Several of the 100 wounded were in critical condition.
"On behalf of the United States, I offer our deepest condolences to the families and friends of the dozens of victims of today's murderous attack in Reyhanli," Ricciardone said.
"The United States strongly condemns today's vicious attack, and stands with the people and government of Turkey to identify the perpetrators and bring them to justice."
Two explosive-laden cars blew up in the town of Reyhanli, just a few miles (kilometers) from the main border crossing into Syria.
Turkey's Interior Minister Muammer Guler blamed "groups supporting the Syrian regime and its intelligence services" for carrying out the attack.
Turkish Foreign Minister Ahmet Davutoglu, on a visit to Berlin, said it was "not a coincidence" that these bombings occurred as international diplomatic efforts to solve the Syrian crisis were intensifying.
The United States and Russia -- a rare remaining supporter of the Assad regime -- pledged this week to relaunch efforts to solve the conflict, that Kerry said has claimed 70,000 and 100,000 lives since March 2011.