Arab diplomats say Saudi Arabia has launched a large military incursion across the border into northern Yemen, aimed at ending a Shiite rebellion inside its troubled southern neighbour.

Two diplomats on Thursday, say Saudi Tornado and F-15 warplanes have bombarded targets inside Yemen since Wednesday afternoon, inflicting significant casualties on the Yemeni rebels. The diplomats spoke on condition of anonymity because they are not allowed to speak to the media.

The Arab diplomats say army units and special forces have been sent to northern Yemen, and that several Saudi towns on the border have been evacuated.

Neither Saudi Arabia nor Yemen have confirmed the offensive. But a rebel spokesman told the Associated Press that Saudi warplanes and artillery hit several areas Thursday.

The northern rebels, known as Hawthis, have been battling Yemeni government forces intensively over the past few months in the latest flare-up of a sporadic conflict over the last five years. The Hawthis are based in a northern province that borders Saudi Arabia. Hawthi spokesman Mohammed Abdel-Salam told The Associated Press the Saudi offensive early Thursday hit at least four areas inside Yemeni territory.