A statement by the official Yemeni news agency, Saba, issued as MEI went to press, described the deal as a "final and permanent treaty for marine and land borders".

No details were given, but it said it the agreement incorporated the line adopted by the 1934 Ta’if treaty, which defined the western end of the border, and also covered the remaining (major) part of the 1,500-mile border which has not previously been defined.

The agreement came on the first full day of an official visit to the kingdom by President Ali Abdullah Salih - visit which had been heralded as historic but which was overshadowed and cut short by the death of President Assad in Syria. Salih and Crown Prince Abdullah then left separately for Damascus to attend the funeral.

It became clear that a breakthrough was near when Crown Prince Abdullah, after years of frosty relations between the two neighbours, attended celebrations in Sana’a to mark the tenth anniversary of Yemeni unification on May 22.

There had been speculation that a deal would be signed during the prince’s visit but last-minute hitches, thought to be connected with tribal boundaries in the border area, prevented it.

One so-far-unexplained aspect of the deal is that neither President Salih nor Prince Abdullah put their name to the document. It was signed by the two foreign ministers: Abd al-Qadr Bagammal for Yemen and Prince Saud Al-Faisal for Saudi Arabia.

Details of the agreement were due to be given at a press conference on June 14.

The border quarrel had become an almost permanent feature of Saudi-Yemeni relations which have been characterised by mutual suspicion and claims of interference in each other’s internal affairs.

Whether the border was a root cause of the friction or merely a symptom of it remains to be seen. Yemen has previously attributed many of its internal problems - ranging from kidnappings to the 1994 north-south war - to machinations by the Saudis. Now, either those problems will diminish or Yemen will place the blame elsewhere.