President Omar al-Bashir of Sudan has ordered the border with South Sudan to be opened.
He announced the move on a first visit to the South since its independence.
Speaking alongside his southern counterpart, Salva Kiir, Mr Bashir also called for peace and normal relations.
Tensions between the two countries, strained after they came to the brink of war last year, have eased recently, but disagreements over oil and territory remain.
However, disagreements over oil and territory continue.
“I have instructed Sudan’s authorities and civil society to open up to their brothers in the Republic of South Sudan,” Mr Bashir said in a speech in the southern capital, Juba.
Sudan’s president invited Mr Kiir to Khartoum for further talks and he also addressed worshippers at a mosque in Juba.
“We won’t go back to war,” he said. “President Kiir and I agreed that the war was too long.”
For his part, Mr Kiir said that he and Mr Bashir had agreed to implement all co-operation agreements.
The South’s independence in 2011 – which followed decades of civil war – left key issues unresolved.
South Sudan took with it nearly three-quarters of Sudan’s oil production when it declared independence and the two sides fell out over how much the South should pay to export its oil through Sudanese pipelines.
At the height of the dispute last year, the South shut down its entire oil output, badly hitting both struggling economies.
Oil started flowing again this month after both sides struck a deal in the Ethiopian capital, Addis Ababa, in March, helping to ease tensions.
They also agreed to withdraw troops from their border area.
A demilitarised buffer zone is being set up, with the intention of improving security.
However, the two leaders still need to agree on who owns the flashpoint Abyei province and other regions along their disputed 2,000km (1,200 mile) border.
Territorial disputes, border demarcation and the pipeline fee issue are expected to feature again in future talks.