Abyei has been a main bone of contention between the African neighbours, which came close to all-out war last month when border fighting escalated, the worst violence since South Sudan seceded from Sudan in July.
Last year, Sudan seized Abyei, a region with fertile grazing land and small oil reserves, after an attack on a military convoy blamed by the United Nations on the southern army.
Ban confirmed on Wednesday that the Sudanese army had withdrawn from Abyei as announced by the government but demanded at the same time that police also leave.
Sudanese army spokesman al-Sawarmi Khalid told SUNA that 169 armed policemen would stay until a planned Abyei police force staffed by both countries had been formed.
"There are 169 policemen staying who are equipped with regular arms and can perform duties until the (Abyei) police force agreed by the joint committee has been set up," he said, according to SUNA.
He said Sudan had also left behind police to protect an oil field inside Abyei. Some 3,800 Ethiopian U.N. peacekeepers are currently deployed in Abyei, which is meant to be demilitarised with a civilian administration under a U.N. peace plan.
South Sudan has already withdrawn its troops from Abyei but has kept 20 unarmed security personal in the area, an official told Reuters on Wednesday.
South Sudan's top negotiator, Pagan Amum, told reporters in Addis Ababa that Sudan was deceiving the world with its withdrawal announcement. He called on the U.N. Security Council to take measures against Sudan, without elaborating.
On Tuesday, the two neighbours resumed African Union-brokered talks in Addis Ababa, the first since negotiations were broken off during the fighting last month.
Diplomats expect no quick breakthrough as both sides are at loggerheads over a long list of disagreements - from marking the disputed border and deciding on the status of Abyei to agreeing on oil export fees for South Sudan.
The landlocked new nation inherited much of Sudan's oil reserves, but shut down production in January to stop Khartoum taking oil for what the latter called unpaid export fees.
Oil is the lifeblood of both economies, and accounts for about 98 percent of South Sudan's state revenues.