(CNN) -  Turkey fired on Syrian government targets in response
to the shelling of a Turkish border town in which five civilians
were killed Wednesday, according to Prime Minister Recep Tayyip
Erdogan's office.  The town of Akcakale "was hit by artillery
fire belonging to the Syrian regime forces," a statement from
Erdogan's office said, in the first clear assertion of blame for
the shelling.  "Our armed forces on the border responded
immediately to this atrocious attack within the rules of
engagement, and points in Syria determined by radar were hit
with artillery fire," it said. "Turkey, within the confines of
the rules of engagement and international law, will never leave
these types of provocations aimed at our national security
unanswered."  The retaliatory artillery fire marks a significant
increase in tension between the two countries, and CNN affiliate
CNN Turk reported that witnesses observed intermittent artillery
fire from Turkey into Syria continuing into the early hours
Thursday.  Syrian authoriti