Residents of a Turkish border town hid inside their homes Saturday after three Syrian shells landed inside Turkey in separate incidents amid fierce fighting in Syria.

The shelling prompted Turkish forces to return fire as clashes between the two neighbors entered a fourth day, according to government and semi-official media reports.

As Turkish forces deployed along the border, Foreign Minister Ahmet Davutoglu warned that "any future attack on Turkey from anywhere will be silenced," according to the semi-official Anadolu Agency news service.

The Syrian shells hit outside two villages in Hatay province, the provincial government said in statements.

One shell landed about 50 meters (164 feet) into Turkey. In the second incident, a shell landed about 1.2 kilometers (0.75 miles) into Turkey, between a Turkish village and a border post, the provincial government said.

In both cases, authorities believe Syrian troops were firing on rebel forces stationed near the border.

The Anadolu Agency news service said three shells had been fired Saturday into Turkish territory.

Turkish border troops retaliated, firing twice into Syrian territory, the Hatay government said.

U.S. Defense Secretary Leon Panetta expressed concern about the cross-border activity.

"The fact is, there is a war going on in Syria between the opposition and the regime forces, and it's one that has cost a large number of lives," he told reporters in Lima, Peru. "Whether or not that conflict begins to extend into the neighboring countries such as Turkey remains to be seen, but obviously the fact that there are now exchanges of fire between these two countries raises additional concerns that this conflict could broaden."

The shelling comes amid fighting between rebel and regime forces over the nearby Syrian border village of Khirbet al-Jouz. Rebel forces captured the village Saturday after seven hours of fighting, according to the London-based Syrian Observatory for Human Rights.

At least 40 Syrian soldiers and nine rebels were killed in clashes in Khirbet al-Jouz and in the Jisr al-Shughur countryside, in Idlib province, the group said.

Residents across the border in Turkey could see and hear gunfire from the fighting, and government officials took to village loudspeakers to warn residents not to go outside.

"How can we not be afraid? Listen you can hear the gun-fighting," said resident Hamza Tuncer.

Tuncer said he helped carry the bodies of two dead fighters into the village.

One was a fighter who suffered a foot wound but decided to return to the battle, Tuncer said.

"That's when he got shot in the head," he said.

In addition to the shelling, fires from forests burned in the conflict have spread to the Turkish side of the border, leaving the air filled with smoke, resident Turhan Tomak said.

"We have no forest left. It hurts my insides. All our forests are gone," Tomak said.

The back-and-forth shelling between Syrian and Turkish forces began Wednesday when a shell fired from Syria hit the Turkish town of Akcakale, killing five civilians and injuring nine others.

Davutoglu said he was certain the shells that hit Turkey on Saturday came from the Syrian army because it is a type used only by that country's forces.

His warning against Syria comes amid a buildup of forces along the Syrian border. Armored units have deployed to several areas along the border, the Anadolu Agency reported.

The Turkish parliament has approved a resolution allowing military forces to deploy abroad, but government officials have said they do not want war with Syria, once a close ally.

But Turkish Prime Minister Recep Tayyip Erdogan has warned Syria not to escalate tensions.

"It would be a deadly mistake to test Turkey's deterrence, determination and capacity," he said.