Israeli warplanes struck Gaza early Thursday, drawing retaliatory rocket fire from Palestinian militants, as violence flared despite US calls for "urgent steps" to restore calm.

Israel said the pre-dawn strikes were in response to an earlier rocket launch and targeted military training camps used by Gaza's Islamist rulers Hamas.

A statement from the Israeli military said fighter jets had "struck a production site for raw chemical material production, preservation and storage along with a weapon manufacturing site" belonging to Hamas.

The strikes came "in response to the rocket launch from the Gaza Strip into Israel earlier" Wednesday.