UNITED NATIONS - A senior U.N. peacekeeping official said Thursday that fighting had escalated in parts of South Sudan, despite a government-declared unilateral cease-fire in May.

"There have been concerning reports of active military operations in the Equatorias and Upper Nile," U.N. deputy peacekeeping chief El Ghassim Wane told the Security Council.

"The security environment remains extremely volatile and South Sudan is in need of an effective and credible cease-fire," he said.

Wane said earlier this month that the U.N. peacekeeping mission in South Sudan had received credible reports of heavy fighting after the Sudanese army moved toward Mathiang in Upper Nile. He said there were also clashes between government and opposition forces near Torit, in Eastern Equatoria.

"The nature of these operations clearly contradicts the unilateral cease-fire declared by the government," he said.

Last August, the Security Council authorized the deployment of 4,000 additional peacekeepers as part of a Regional Protection Force. They will be based in the capital, Juba, to help protect civilians.

Deployment has been slower than envisioned. Wane told the council that troops from Rwanda and Ethiopia should be arriving in the next two months.

South Sudan's rebel leader Riek Machar addresses a FILE - South Sudan's rebel leader Riek Machar addresses a news conference in Ethiopia's capital Addis Ababa, Oct. 18, 2015. FILE - South Sudan's rebel leader Riek Machar addresses a news conference in Ethiopia's capital Addis Ababa, Oct. 18, 2015.

Revitalizing peace process

Meanwhile, efforts to revive the stalled peace process continue.

Former Botswana President Festus Mogae, who chairs the Joint Monitoring and Evaluation Commission, which is overseeing peace efforts in South Sudan, told the council via a video link from Juba that he had engaged in extensive outreach to stakeholders and regional leaders.

Among those he met with recently was former South Sudan Vice President Riek Machar, who is the political rival at the center of the more than three-year-old conflict with President Salva Kiir. Machar is living in South Africa.

Mogae told the council, "The message I conveyed to Dr. Riek Machar was to renounce violence, declare a unilateral cease-fire and participate in the national dialogue" — an initiative begun by Kiir to try to reconcile all grievances of South Sudan's political and armed groups. "He declined to do so," Mogae said. "However, he demanded a new political process by the region outside South Sudan."

Also of concern is the obstruction of humanitarian aid deliveries by both the government and opposition. More than 6 million South Sudanese are severely food insecure.

In June, council diplomats said aid was blocked 100 times, the worst month for aid access this year. In addition, the government is still asking humanitarian groups to pay high fees to continue operating in the country.

U.S. Deputy Permanent Representative to the U.N. M FILE - U.S. Deputy U.N. Ambassador Michele Sison is pictured at a Security Council session, Feb. 2, 2017. FILE - U.S. Deputy U.N. Ambassador Michele Sison is pictured at a Security Council session, Feb. 2, 2017.

Sanctions, arms embargo

"This council must be prepared to hold the parties accountable for their inaction and for the continued suffering of South Sudan's people," U.S. Deputy U.N. Ambassador Michele Sison told the council. "The council must put real pressure on the parties to change their behavior. That should start with additional targeted sanctions and an arms embargo."

She said imposing such measures would show that the Security Council was serious about pushing for an end to the fighting and a return to the negotiating table.

A U.S.-led effort in the council last December to impose an arms embargo on South Sudan failed, with only seven of the 15 council members supporting the measure and the other eight abstaining.

"I haven't seen a significant enough change to be confident that there would be nine positive votes and no vetoes this time around," British Ambassador Matthew Rycroft told reporters when asked about a possible move to try again for an arms embargo.

Since fighting along largely ethnic lines erupted between forces loyal to Kiir and Machar in December 2013, tens of thousands of people have been killed and more than 2 million have been displaced from their homes.