KAMPALA, UGANDA — Grace Asamo was shocked when soldiers from South Sudan detained her and eight other members of the Uganda parliament.
"They attacked our vehicles with stones and guns and told us not to return," said Ms. Asamo, who represents the Eastern Region of Uganda.
The Ugandan lawmakers said they were within the recognized boundaries of their own country, while the South Sudanese soldiers had strayed across the border.
The assault on the Ugandan legislators on a fact-finding mission last week was the latest flare-up in a long-running border dispute that dates back years before South Sudan became the world's newest nation in July 2011.
The squabble, which South Sudan inherited from Sudan, is threatening security and trade between Uganda and its northern neighbor.
The border region, ravaged by war, has a history of land-grabbing, illegal construction, deforestation, kidnappings and racketeering.
The row has also become an outlet for South Sudanese frustration over an influx of Ugandan merchants. Seventy thousand Ugandans are estimated to be working in South Sudan.
Uganda, like most African nations, adheres to post-colonial borders, which would have found the Ugandan legislators inside Uganda at the time of the attack.
However, many South Sudanese claim traditional boundaries, which place portions of Uganda some 10 miles inside the South Sudan state of Central Equatoria.
Sarah Bol, the top diplomat at the South Sudanese Embassy in Kampala, said the Ugandan legislators had passed illegally into Kajo-Keji county in South Sudan at the time of the attack.
Ms. Bol and Ambassador James Mugume, permanent secretary in Uganda's Foreign Affairs Ministry, said Ugandan President Yoweri Museveni and South Sudanese President Salva Kiir will resolve the issue within next several months, although no official meeting date has been set.
Violent border disputes erupted even before South Sudan gained its independence from Sudan.
Tensions flared in 2005, when Sudanese authorities stopped Ugandans from constructing a road and communications tower along the border.
Sixty-five Ugandans have been murdered in the border region since 2007, according to the Joint Action for Redemption of Uganda Traders in Sudan.
Ugandan authorities accused Sudan of detaining and torturing 20 Ugandans in 2009.
Ms. Bol disputes the figures and said Ugandans are welcomed in South Sudan where they are generally safe to work. She said Ugandan media often sensationalizes border incidents.
Even if a boundary is agreed upon, tensions are unlikely to ease.
Law enforcement in South Sudan is weak, and resentment is high, as Ugandans rush in to fill jobs that South Sudanese, hobbled by decades of war with Sudan, cannot do on their own.
Food shortages allows Ugandans to sell produce at double what they can fetch back home.
South Sudan is now Uganda's largest export market, as Ugandans cut inroads into agriculture, light manufacturing and construction.
South Sudan citizens crossing into Uganda benefit from education, health and other basic services. Uganda's private sector is reportedly lobbying for the construction of a railway to link the countries.
Frederick Ssenonga of the Joint Action for Redemption of Uganda Traders said intimidation, robbery, shootings and stolen funds are part of the cost of doing business in South Sudan. He claims to have lost $142,000 in construction investments and that both governments have failed to uphold the law.
Ms. Bol said a vicious oil dispute between South Sudan and Sudan has sapped the new nation's ability to establish security and rule of law. Tribal tensions in the eastern part of South Sudan are also creating instability.
South Sudan offers "high risks and high profits," as Mr. Mugume described trade prospects in South Sudan.