Wathiq al-Battat, the head of the pro-Iranian Shiite group Jaish al-Mukhtar, said by telephone from Baghdad that the attack was "a warning strike" to Saudi Arabia to stop "interfering" in Iraqi affairs, Reuters reported.

"We did not mean for our missile to reach a residential area because we value people's blood," said Battat. "But next time, if Saudi Arabia continues the same course, we will go farther, little by little."

Diplomats and Iraqi security officials routinely say they do not believe Jaish al-Mukhtar to be a capable militia and do not regard Battat as a credible figure.

But the incident comes amid regional turmoil fuelled by the Syrian conflict.

Earlier Thursday, Saudi state news agency SPA quoted border guard General Mohammed al-Ghamidi as saying six mortar rounds hit Wednesday "in an uninhabited area near Al-Awja border crossing... in Hafr al-Batin in Eastern Province, and no damage was caused."

Residents said Saudi warplanes were flying over the area early on Thursday and Ghamidi said Saudi authorities were in "direct contact" with their neighbors to identify the source of the shelling and to prevent a repetition.

Okaz newspaper's website said the mortar fire came "from the Iraqi side of the border."

Ghamidi added that his men had entered Hafr al-Batin, "an oil-rich area and vital to the Saudis."

Hafr al-Batin, which also borders Kuwait, was a command headquarters for US forces during the 1991 Persian Gulf War, which expelled Iraqi occupation forces from the emirate.

BA/BA