The blasts, which were 15 minutes apart and hit the town of Reyhanli's busiest street, raised fears that Turkey could increasingly be drawn into Syria's brutal civil war.
Turkey already hosts Syria's political opposition and rebel commanders, has given shelter to hundreds of thousands of Syrian refugees and in the past retaliated against Syrian shells that landed in Turkey.
"We know that the Syrian refugees have become a target of the Syrian regime," Deputy Prime Minister Bulent Arinc said. "Reyhanli was not chosen by coincidence."
"Our thoughts are that their mukhabarat (Syrian intelligence agency) and armed organizations are the usual suspects in planning and the carrying out of such devilish plans," he said.
Arinc said the attacks were still being investigated, but that If it's proven that Syrian was behind the attack, Turkey would "do whatever is necessary," without specifying if that included military action.
One of the car bombs exploded outside the city hall while the other went off outside the post office. Reyhanli, a main hub for Syrian refugees and rebels in Turkey's Hatay province, is just across the border from Syria's Idlib province.
Images showed people frantically carrying the wounded through the rubble-strewn streets to safety. Black smoke billowed from a tall building.
The explosions came days before Prime Minister Recep Tayyip Erdogan is scheduled to travel to the U.S. for talks, which are expected to be dominated by the situation in Syria. The car bombings also follow allegations by Erdogan the Syrian regime has fired about 200 missiles tipped with chemical weapons.
Syrian mortar rounds have fallen over the border before, but if the blasts turn out to be linked to Syria it would be by far the biggest death toll in Turkey related to its neighbor's civil war.
Syria shares a more than 500-mile (800-kilometer) border with Turkey, which has been a crucial supporter of the Syrian rebel cause. Ankara has allowed its territory to be used as a logistics base and staging center for Syrian insurgents.
Another deputy prime minister, Besir Atalay, said 42 people were killed and 140 others were wounded in the blasts. There was no immediate information on the identities or nationalities of the victims.
Erdogan had earlier raised the possibility the bombings may be related to Turkey's peace talks with Kurdish rebels meant to end a nearly 30-year-old conflict, but most of the suspicions link the attacks to Syria.
The bombings" will increase the pressure on the U.S. president next week to do something to show support to Turkey when Erdogan visits him in Washington," said Soner Cagaptay, an expert on Turkey at the Washington Institute. "Washington will be forced to take a more pro-active position on Syria, at least in rhetoric, whether or not there is appetite for such a position here."
Salman Shaikh, director of the Brookings Doha Center, said the attack may force Turkey to take action.
"It should be a defining moment for Turkey," Shaikh said. "It has been supporting the rebels, and there has been strong rhetoric. But this may be a moment where it really has to assert itself - if it is the Assad regime (behind the bombings), and it is quite conceivable it is."
Turkey's opposition criticized the government's policy on Syria, saying its active support of the rebels had put the country's security at risk.
"Erdogan's discourse of hatred toward Assad and provocations against the administration in Damascus is coming back to us in the form of attacks and provocations," said Devlet Bahceli, chairman of a nationalist opposition party.
The force of Saturday's explosions gutted some buildings, and the charred shells of cars littered the streets.
"Three buildings partly collapsed and became unusable," Talat Karaca, who witnessed the second explosion from his rooftop, told The Associated Press by telephone. "We couldn't approach the scene for a long time because of the blaze."
Khawla Sawah, the medical director of the Union of Syrian Medical Relief Organizations in Reyhanli, said the town's main hospital was full and many of the wounded were taken to the nearby city of Antakya and to a clinic set up by the Syrian medical relief group on Reyhanli's outskirts. The center received 11 wounded, including one Turk and 10 Syrians.
She said some of the injured told her that the cars that exploded had Syrian license plates.
Both Sawah and another witness, Suzan Alhasoglu, said the incident raised tension in Reyhanli with angry youths attacking Syrians cars and other targets.
"The authorities are asking Syrians to stay home and not drive around in Syrian cars," Sawah said. "Syrian doctors at the Reyhanli hospital were asked to go home too."
Turkey's military released a statement condemning the attack and Foreign Minister Ahmet Davutoglu vowed from Berlin that Turkey would act.
"Those who for whatever reason attempt to bring the external chaos into our country will get a response," he said.
The U.S. Embassy in Ankara issued a statement condemning the "murderous attack" in Reyhanli and said Washington "stands with the people and government of Turkey to identify the perpetrators and bring them to justice."
The main Syrian opposition group, the Syrian National Coalition, condemned the attack and said it stands together with the "Turkish government and the friendly Turkish people."
The coalition sees "these heinous terrorist acts as an attempt to take revenge on the Turkish people and punish them for their honorable support for the Syrian people," it said.
The frontier area has seen heavy fighting between rebels and the Syrian regime. In February, a car bomb exploded at a Syrian border crossing with Turkey, just a few kilometers from Reyhanli, killing 14. Turkey's interior minister at the time blamed Syria's intelligence agencies and its army for involvement.
Four Syrians and a Turk are in custody in connection with the Feb. 11 attack at the Bab al-Hawa frontier post. No one has claimed responsibility, but a Syrian opposition faction accused the Syrian government of the bombing, saying it narrowly missed 13 leaders of the group.
In that bombing, most of the victims were Syrians who had been waiting in an area straddling the frontier for processing to enter Turkey.
Tensions also flared between the Syrian regime and Turkey after shells fired from Syria landed on the Turkish side, prompting Germany, the Netherlands and the U.S. to send two batteries of Patriot air defense missiles each to protect their NATO ally.
Suzan Fraser reported from Ankara. Associated Press writers Ezgi Akin in Ankara, and Bassem Mroue, Yasmine Sakher and Karin Laub in Beirut contributed to this report.