"There is not enough food now", Rev Ezekiel said, "People are hungry".
South Sudan has been embroiled in civil war for over three years.
Across South Sudan, at least 7.5 million people, nearly two thirds of the population, need humanitarian assistance, WFP said.
The objective of the summit was to urge both the governments of Sudan and South Sudan into making certain that their territories were not used by armed groups that pose a threat to the security of both counties, as well as to implement the Agreement on the Resolution of the Conflict in the Republic of South Sudan (ARCSS).
The starvation in South Sudan was attributed to many reasons including the civil war and collapse of the economy in the new-born state.
The four South Sudanese and three Kenyans worked for a local non-governmental organization called GREDO (Grass Roots Empowerment for Development Organization) and were attacked while on a routine food convoy from Juba, the capital, to Pibor.
"I would like to send my condolences to the family, friends and colleagues of these dedicated aid workers", he added.
"We strongly condemn and denounce the killing of the six humanitarian actors who have come here to help the people and yet they have been killed", the Chairperson of the AU Commission, Moussa Mahamat, told reporters in Juba.
"We call for an independent investigation into the heinous and senseless of the aid workers and perpetrators must be brought to justice", it said.
The attack marks the deadliest incident targeting humanitarian organisations since the country's civil war began.
Around 7.5 million people are in need of humanitarian assistance in South Sudan, according to the United Nations, in the midst of a man-made starvation.
"The humanitarian workers were travelling in a auto that was clearly marked as belonging to a non-governmental organisation, including NGO number plates".
At least 79 aid workers have been killed in South Sudan since December 2013, including at least 12 this year. With social workers and humanitarian organisations attacked, the situation could worsen for the famine-hit country.
The United Nations welcomed Sudan's decision to open the aid corridor, saying it showed Khartoum's "commitment" to the people of South Sudan.
The bodies of the slain aid workers were found on the road by other members of the convoy who were some way behind, Shearer said in a statement seen by Anadolu Agency.
"The latest attack occurred in areas controlled by the South Sudan government", said Shearer, adding: "The government needs to investigate and apprehend the offenders". The aid workers were travelling from Juba to Pibor.
Malaysia says Kim Jong Nam's body still in Kuala Lumpur
Relations between Malaysia and North Korea have frayed since Kim's death, with each expelling the other's ambassador. North Korea then blocked all Malaysians from leaving until a "fair settlement" of the case was reached.
NCAA Tournament wrap: UNC edges out Kentucky on Maye game-winner
South Carolina , a team that finished third in a maligned SEC, hadn't won an NCAA tournament game in 44 years until nine days ago. There are team activities, lots of media commitments and constant attention. "Now we just need to go and continue to play well".