The Israeli army says air raid sirens have sounded in the Golan Heights.
The sirens went off shortly after the Syrian state news agency and activists reported rocket fire from Israel into southern Syria just before midnight Wednesday.
The Israeli army says it is investigating and has no further details.
The Britain-based Syrian Observatory for Human Rights says aircraft flew over the Israeli-occupied Golan Heights, adjacent to southern Syria. There are no immediate reports of airstrikes.
Israel's military has been on heightened alert in recent days, fearing an attack from Syria. Syria and Iran have accused Israel of carrying out a series of airstrikes on Iranian targets in Syria in recent weeks. Israel has not confirmed or denied involvement.