Two car bombs exploded in Reyhanli, Turkey, Saturday.
There has been no immediate claim of responsibility for the attack.
Turkey supports the uprising against Syrian President Bashar al-Assad.
The explosions were reported near the city's town hall and post office.
The Turkish foreign minister told reporter, "There may be those who want to sabotage Turkey's peace, but we will not allow that."
In addition to the 20 killed, 46 have been injured, many seriously, and officials say the death toll could rise.
The region has faced attacks recently. In February, a bus exploded at a border crossing outside Reyhanli.
Turkish Prime Minister Tayyip Erdogan, who is meeting with Obama next week, said Turkey would support a U.S.-enforced no-fly zone in Syria.
