Yesterday, military sources in the northern capital, Sanaa, said that they had captured the airport on the outskirts of Aden, which serves as an air base for the small but hitherto effective southern Yemeni air force.
At the same time, sources in Sanaa said northern forces had captured al-Mukalla, the capital of Hadramawt province, 600 km (380 miles) east of Aden, where the southern leader and Vice-President of the old united republic, Ali Salem al-Beidh, fled earlier in the fighting. Southern sources denied these allegations.
A Reuters correspondent visited the airport outside Aden and said it was still in southern hands. The reporter said that later yesterday a second assault backed by tanks was made on the airport by northern troops, but was meeting stiff resistance. Southern sources said a small group of northern troops penetrated the outskirts of al-Mukalla, but were repulsed.
But there is no disputing the trend: northern forces are moving slowly but relentlessly to crush the secessionist rebellion.
On Monday, northern artillery mounted its heaviest bombardment so far on Aden. At least 41 people were killed in the shelling. The city is hard pressed to cope with the continuing siege.
The pre-war population of 350,000 has been swelled by an influx of 50,000, fleeing the fighting in the hinterland. Fuel, food and water are in short supply. The main water pumping station and pipelines have been damaged and the International Red Cross has been unable to repair them.
The capture of Aden would spell the effective end of southern hopes of seceding from the united Yemen, four years after the two countries came together. Already the southern leadership is reported to be on the run.
Mr Beidh is variously reported to be in Oman, Moscow, Kuwait and Cairo, although there is no official confirmation he has left al- Mukalla.
The advance of northern forces has overthrown the conventional wisdom that the north was not strong enough to impose a military solution, that a negotiated settlement would have to be sought. The various ceasefires - the latest brokered by the Russian Foreign Minister last week - have seldom held more than a few hours. Diplomatic initiatives have dribbled into the sand.
The main support for the south has come - despite its Socialist political leadership - from Saudi Arabia and most members of the Gulf Co-operation Council (GCC). They wish to punish the northern leadership for supporting Iraq after its invasion of Kuwait in 1990.
The foreign ministers of the six members of the GCC met in Kuwait yesterday together with the two Arab states - Egypt and Syria - which had backed the GCC's drive to remove Iraqi forces from Kuwait three years ago.
The southern Yemenis had hoped the meeting would formally recognise the breakaway Democratic Republic of Yemen (DRY). But at this stage it would do little to change realities on the ground.
Furthermore, the south is divided between the cosmopolitan Adeni community, the apparatchiks of the Yemen Socialist Party, and the mercantile classes of the Hadramawt.
Arab analysts are now looking at the post-war settlement. One theory is that when the Yemeni Socialist Party is crushed, the country will revert to a confrontation between two political forces: the party of President Ali Abdullah Saleh and the fanatical, tribally based, Islamic traditionalists of the Islah party, who oppose all traces of modernity or Socialism.