Mustafa Guclu, a witness in Akcakale, said the Turkish military fired five rounds of artillery "after midnight" toward Syria and another round around 5 a.m. on Thursday.
"I have not heard any more shelling since then," he told the Associated Press.
The Syrian mortar shell damaged the door and walls of a house in Akcakale, while shrapnel poked holes and shattered windows of neighboring houses and shops.
Some residents of Akcakale abandoned their homes close to the border and spent the night on the streets.
Turks have grown weary of the burden of involvement in the Syrian conflict, which includes the hosting of 90,000 Syrian refugees in camps along the border.
Yet Turkey is still loath to go it alone in Syria, and is anxious for any intervention to have the legitimacy conferred by a U.N. resolution or the involvement of a broad group of allies. Turkey is mindful in part of inconclusive ground missions, mostly in the 1990s, against Kurdish guerrillas based in northern Iraq, as well as the bitter lessons of being seen as an occupying power that are associated with the U.S.-led invasion in Iraq.
Reaching deeper into history, Turkey is aware of Mideast sensibilities over Ottoman rule over much of the region.
On a visit to Pakistan on Thursday, Russian Foreign Minister Sergey Lavrov expressed his government's concern over the escalation of tensions.
Lavrov, speaking at a press conference in Islamabad, said Syria has assured Russia, an ally, that such an incident as the shelling that killed the Turks will not happen again.
"It is of great concern for us," Lavrov said. "This situation is deteriorating with every coming day."
Germany's foreign minister, Guido Westerwelle, said NATO members agree on the need for solidarity but also on prudence in reacting to events on the Turkish-Syrian border.
The Turkish retaliatory shelling and steps to authorize possible military intervention against Syria were the latest events to sharply escalate tensions between the two former allies.
In June, Turkey reinforced its border with anti-aircraft missiles and threatened to target any approaching Syrian military elements after Syrian forces brought down a Turkish jet, killing its two pilots. Turkey said the plane was in international airspace, countering Syrian claims that it was in Syrian airspace.
Fraser reported from Ankara, Turkey. Associated Press writers Christopher Torchia in Istanbul, Elizabeth Kennedy in Beirut and Nahal Toosi in Islamabad contributed