The number of foreign visitors coming to Turkey tumbled 10 percent in February, the biggest drop in a decade, data showed on Tuesday, as widening security concerns ate into a major source of revenue for the economy.

Turkey has been hit by a spate a bomb attacks this year, including two blamed on Islamic State (ISIS) in Istanbul, its biggest city and traditional tourist draw. In January a suicide bomber blew himself up in the city’s historic heart, killing 12 German tourists.

Tourist interest in Turkey could drop further after another suicide bomber blew himself up on Istanbul’s most popular shopping thoroughfare this month, killing three Israeli tourists and an Iranian. This week Israel warned its citizens visiting Turkey to leave “as soon as possible”, predicting possible follow-up attacks.

Tourism fell by 10.32 percent year-on-year in February, to 1.24 million people, the data from the tourism ministry showed.

The decline was the biggest since October 2006. The industry is also suffering from a chill in relations with Russia – typically a major source of tourism revenue for Turkey – and Russian visitors fell by more than half during the month.

Relations between Moscow and Ankara have worsened after Turkey shot down a Russian jet over Syria last year.

Economists have forecast that tourism revenue will drop by a quarter this year, costing the country around $8 billion.