Turkish troops have returned fire after cross-border shelling from Syria for the sixth day in a row.
A Syrian shell landed on Turkish territory in the border province of Hatay, prompting immediate retaliatory strikes.
Earlier the state-run Turkish Anadolu agency said the shell landed on a cotton field near the town of Altinozu. People were working on the field, but no one was injured.
Turkey and Syria have been firing artillery and mortars across their volatile border since Wednesday after shelling from Syria killed five civilians.
Turkish President Abdullah Gul called on the international community to do more to try to end Syria's nearly 19-month-old conflict, which has claimed more than 30,000 lives and - with Turkey-Syria tensions rising - heightened fears of a regional conflagration.
UN chief Ban Ki-moon also warned that the escalating conflict on the Syrian-Turkish border is "extremely dangerous."
The main Syrian opposition group, meanwhile, signalled it is softening its position on possible talks to arrange a political transition.
In the past, the Syrian National Council has said that president Bashar Assad and his inner circle must step down before such talks can begin. However, the SNC chief said that talks would now be possible with members of the regime who do not have blood on their hands.
The persistent Syrian shelling suggests the cross-border fire of recent days is not accidental. Turkey, along with other foreign allies of the Syrian opposition, is reluctant to intervene militarily in Syria, and Damascus' military strategy relies, in part, on the high threshold for foreign intervention.
Mr Gul described Syria's civil war and its regional impact as the "worst-case scenario that we've all been dreading," adding that along with the suffering of the Syrian people, "once in a while we're also affected."
He also said the situation in Syria must not be allowed to continue.
"Sooner rather than later there will be change, a transition," he said. "Our only hope is that this happens before more blood is shed, and before Syria self-destructs more than it already has. It's also crucial that the international community act in a more effective way."
Efforts to get the two sides to negotiate a peaceful transition have failed up to now.
Activists reported violence in different parts of the country, mostly in the central city of Homs, the northern city of Aleppo, and the southern region of Daraa.
The Syrian Observatory for Human Rights, a British-based activist group, said 20 people were killed in the southern village of Karak, which has been attacked by government troops. It said the 20 were killed when vehicles transporting wounded people were targeted by troops.
Meanwhile, residents of the Turkish border town of Akcakale, struck repeatedly by shelling from Syria, said they fear for their safety, even though Turkish troops have deployed to the area.
"If this shelling is going to continue day in and day out, we can't live here. We are not safe, our property is not safe," said Hamit Ciftcioglu, whose jewellery store is near where a mortar round hit on Sunday.