BRUSSELS – NATO is ready to defend Turkey, the alliance’s top official said Tuesday in a direct warning to Syria after a week of cross-border artillery and mortar exchanges dramatically escalated tensions between the two countries.

Ankara has sent additional fighter jets to reinforce an air base close to the frontier with Syria where shells killed five Turkish civilians last week, sparking fears of a wider regional crisis. Syria has defended its shelling of neighboring Turkey as an accidental outcome of its 18-month-old civil war.

The comments by NATO Secretary-General Anders Fogh Rasmussen were the strongest show of support to Turkey since the firing began Wednesday – though the solidarity is largely symbolic.