Israel said it carried out airstrikes early on Wednesday against Iranian forces near the Syrian capital, in response to an Iranian attack on Israel a day earlier, potentially escalating tensions along Israel’s northeastern border. The strikes killed at least 21 people, according to a rights monitoring group.

The Israel Defense Forces said in a statement that the strikes near Damascus were focused on Iranian and Syrian “terror targets,” and noted that a Syrian air defense missile had been fired in retaliation “despite clear warnings to refrain from such fire.”

“As a result, a number of Syrian aerial defense batteries were destroyed,” the statement read.

There have been sporadic flare-ups across the old Israeli-Syrian armistice line. Israel has clashed there with Syrian and Iranian forces based in Syria as Iran’s influence has grown in the war-torn nation.