President Omar Hassan al-Bashir promised on Thursday that Sudan would respond robustly to what he believes was an Israeli bombing of a Khartoum arms factory.

Bashir, in a speech from the Sudanese embassy in Saudi Arabia broadcast on Sudan's Blue Nile TV, also said he was in "perfect health" after undergoing surgery in the Gulf kingdom.

Sudan last month accused Israel of carrying out an air strike on the Yarmouk weapons plant in the south of Khartoum, causing a blast that killed four people.

Israel has not commented. It has long accused Sudan of channelling weapons from Iran to the Hamas-controlled Gaza Strip, a small Palestinian territory it has under blockade.

"Israel will remain the number one enemy, and we will not call them anything except the Zionist enemy," Bashir said in his speech, shown in footage dated Thursday and his first appearance since undergoing surgery.

Bashir also lamented what he described as Israel's superior, radar-evading aircraft technology, but ruled out normalising relations with the Jewish state.

In a brief text message sent to mobile phones, state radio earlier quoted Bashir as saying he was in "perfect health" and that the response to Israel would be "painful".

Bashir, who came to power in a bloodless 1989 coup, left hospital in Saudi Arabia on Wednesday after undergoing a "small, successful" operation, state media said.

Sudanese blogs and newspapers had begun to speculate about Bashir's health because he has held fewer public rallies in the past few months. He underwent surgery on his vocal cords in Qatar in August, an official said last month.

In the televised speech, Bashir said his surgery and the related medical examinations had taken only 24 hours.

Over 23 years in power, Bashir has weathered multiple armed rebellions, years of U.S. trade sanctions, an arrest warrant from the International Criminal Court, waves of student protests and the secession of oil-producing South Sudan last year.

He is known for his fiery speeches and for dancing and waving his walking stick at public events.