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"Reports about last night's Iranian attacks against Israeli army posts from inside Syria to which Israel responded by striking against Iranian targets in Syria are extremely worrying," the European External Action Service (EEAS) said in a statement.
The deadly strikes by Israel have raised fears of a dramatic increase in regional tensions.
But the situation remains shrouded by conflicting accounts and uncertainty.
"As the EU has said repeatedly, Israel has the right to defend itself," the statement added.
"At the same time, we call on all regional actors to show restraint and avoid any escalation, which could further undermine regional stability."