Turkey says its armed forces have fired on targets inside Syria in retaliation for a Syrian mortar attack that killed five Turkish civilians in a Turkish border town.

Turkish Prime Minister Recep Tayyip Erdogan's office said Turkish forces responded “immediately” by using radar to shell the sources of the Syrian mortar fire.

Mr. Erdogan said Ankara acted within international law and will never fail to retaliate for what he called Syrian provocations against Turkey's national security.

Turkish authorities said a woman and her three children were among those killed when Syrian mortars struck a residential area in Akcakale on Wednesday. They said at least 10 other people were wounded.

Syrian Information Minister Omran Zoabi said Damascus is investigating the origin of the mortar fire. He said Syria offers its condolences to the Turkish people for the deaths in Akcakale.

Zoabi also called on neighboring states to control their borders with Syria to prevent “terrorists” from crossing into Syrian territory. Syria uses the term “terrorists” to describe rebels fighting an 18-month uprising against autocratic Syrian President Bashar al-Assad.

U.S. Secretary of State Hillary Clinton said Washington is “outraged” at the Syrian mortar strike on Turkey, a fellow member of the NATO alliance.

Turkish media said the government will ask parliament on Thursday to approve a bill authorizing more cross-border military operations in Syria. Turkey already has a law authorizing military intervention against separatist Kurdish rebels based in northern Iraq.

Ankara also sent the U.N. Security Council a letter calling for “necessary action” to stop “aggression” by Syria. U.N. diplomats said the Council was discussing a possible statement in reaction to cross-border attacks.

U.N. Secretary-General Ban Ki-moon called on Syria to respect the territorial sovereignty of its neighbors. He said the escalation shows how the Syrian conflict is increasingly harming neighboring states.

Mr. Ban's office said the U.N. chief discussed the situation with Turkish Foreign Minister Ahmet Davutoglu. It said Mr. Ban “encouraged the minister to keep open all channels of communications with Syrian authorities, with a view to lessening any tension that could build up as a result of the (Akcakale) incident.”

The U.S. Defense Department said the Akcakale incident is another example of what it called the “depraved behavior of the Syrian regime.” It said the United States stands by Turkey as a “strong ally.”

NATO ambassadors held an urgent meeting in Brussels Wednesday at Turkey's request, and issued a statement demanding the “immediate cessation of such aggressive acts against an ally.” NATO also urged the Syrian government to “end flagrant violations of international law.”

Earlier Wednesday, four bombs struck a government-controlled section of Syria's largest city, Aleppo, killing dozens of people and wounding nearly 100 others.

The blasts damaged a military officers' club and a nearby hotel that residents said housed pro-government militiamen. Opposition groups said at least 48 people were killed, mostly from the security services, while Syrian state media put the death toll at 31. There was no independent confirmation of casualties.

Aleppo has seen increased fighting between government and rebel forces in recent weeks, but neither side appears to have made significant gains. The city is divided between Mr. Assad's forces mainly in the west and rebels in the east.

VOA's Scott Bobb traveled to the Bab al-Salama camp for internally displaced Syrians, located just a few kilometers from the Turkish border town of Killis. He said about 6,000 Syrians fled to the camp in the past month.

“This upsurge occurred about a month ago when the bombing intensified by the Syrian air force on basically defenseless towns and civilians in northern Syria. People [were] just panicked and traumatized and decided to get out.”

Bobb said the mostly Sunni Syrians initially fled to Turkey, but others were later forced to wait at Bab al-Salama until space becomes available in Turkish refugee camps. He said Turkish officials were letting in hundreds of people each day, with more arriving from deeper inside Syria.

“So it's a constant influx of hundreds, maybe up to a thousand a day at this one point. Multiply that by half a dozen or more crossing points in northern Syria, and you can see why the United Nations is calling it a major catastrophe in waiting.”