Turkey has protested after Syrian forces opened fire across the border, the first such attack since Turkey began housing refugees from the unrest.
Turkey summoned Syria’s envoy to demand such actions stop.
A clash between Syrian rebels and troops spilled over the border, with at least one person killed and a number injured at the Kilis refugee camp.
The violence comes amid fading hopes that a UN-brokered Syria ceasefire will start on Tuesday as planned.
Clashes have continued in Syria despite the truce deal, which requires Syrian troop withdrawals from towns and cities.
The violence showed no sign of abating on Monday, with at least 50 people reported killed. They included at least 12 members of the Syrian security forces who died in clashes close to the Turkish border, the Syrian Observatory for Human Rights group said.
The organisation said said the cross-border incident began with a clash between opposition fighters and Syrian troops at Salameh.
A number of rebels escaped over the border, it said, with Syrian forces continuing to fire on them.
The BBC’s Jonathan Head describes the mood on the Turkish-Syrian border after the shooting
The Observatory said one person later died in the Kilis camp.
The Associated Press news agency quoted Gaziantep provincial Governor Yusuf Odabas as saying that one Turkish translator and a Turkish policeman were among those hurt.
A Turkish foreign ministry official told Reuters: “After this incident the Syrian charge d’affaires in Ankara was called and we demanded an end to this.”
The BBC’s Jonathan Head, on the Turkey-Syria border, says the Syrian army has been careful to keep away from the border but that seems to have broken down this time.
He says incidents like this have inflamed emotions in Turkey and the Turkish government has almost given up on the ceasefire plan, brokered by UN-Arab League envoy Kofi Annan.
Turkey has seen a sharp rise in the number of refugees coming over the border in the past week, and now hosts some 24,000 Syrians, including hundreds of army defectors.
Mr Annan will visit Syrian refugees on the Turkish border on Tuesday, reports say.
A Turkish diplomatic source told AFP news agency: “The visit will only last a few hours, ahead of Annan’s trip to Iran.”
Our correspondent, Jonathan Head, says this is a necessary move by Kofi Annan as there is a diplomatic need for him to show his concern for those who have fled.
However, there are now serious doubts about whether Mr Annan’s ceasefire plan will come into effect on its Tuesday deadline.
Naci Koru, Turkey’s deputy foreign minister, told Turkish television the deadline had become “void at this stage”.
After having earlier agreed to Mr Annan’s plan, Damascus on Sunday called for written guarantees from rebel fighters to end attacks and a promise from foreign states not to fund them.
It said it did not want the rebels to exploit any troop withdrawal to reorganise and rearm themselves.
The rebel Free Syrian Army said although it backed the UN-Arab League truce, it refused to meet the government’s new demands.
China on Monday tried to shore up the plan, with foreign ministry spokesman Liu Weimin calling on the government and opposition in Syria to “honour their commitment of ceasefire and withdrawal of troops”.
But correspondents say Russia, Syria’s main ally, may now have to play a crucial role. Syrian Foreign Minister Walid Muallem travels to Moscow on Monday for talks.
The UN says more than 9,000 people have been killed in the uprising against Mr Assad’s rule which began more than a year ago.
The Syrian government says 2,000 security personnel have been killed in the uprising and blames the violence on “armed gangs” and “terrorists”.