By Denis Dumo and Michelle Nichols

JUBA, Sept 5 (Reuters) - South Sudan still needs to agree the number and nationality of United Nations peacekeepers for a protection force, a government minister said on Tuesday, a day after President Salva Kiir approved the deployment in a bid to avoid a U.N. arms embargo.

Kiir publicly consented to the protection force, authorized by the U.N. Security Council last month, after meeting with council envoys, led by U.S. Ambassador Samantha Power, on Sunday in Juba. However, a joint statement after the meeting noted that the details of the troop deployment still needed to worked out.

Government spokesperson Michael Makuei said on Monday the country also needed to "agree on the armament, we need to agree on the deployment, we need to agree on the time frame."

In the wake of deadly violence in Juba in mid-July between Kiir's troops and soldiers loyal to opposition leader Riek Machar, the Security Council authorized a 4,000-strong regional protection force as part of the 12,000-strong U.N. peacekeeping mission already on the ground, known as UNMISS.

The council has mandated the force until Dec. 15.

"If we don't accept it, if we don't agree with that, nobody will enter South Sudan. Anybody who enters without our consent is 'an invader'," Makuei told reporters.

The council threatened to consider an arms embargo if U.N. Secretary-General Ban Ki-moon reported in mid-September that Kiir's government was not cooperating on the protection force and was still obstructing peacekeepers already on the ground.

"We're going to want to see a significant acceleration in operational discussions about the deployment of the force," Power told Reuters, warning the South Sudanese government not to go back to "first principles or challenging consent."

"There are very conflicting signals because there are some who, if they had a choice, would expel UNMISS tomorrow," Power said. "So the real question is: is there going to be united and consistent follow-through on the direction that the president gave last night by making that commitment?"

East African regional bloc IGAD pushed for a protection force and has pledged to provide troops. South Sudan Minister of Cabinet Affairs Martin Elia Lomoro said on Sunday that the government had no objection to who contributes soldiers.

However, some Security Council diplomats said South Sudan had concerns about some neighboring countries, like Ethiopia, sending troops.

"We have heard some names of the countries which can substitute regional neighboring countries - Zambia, Zimbabwe were mentioned," said Deputy Russian U.N. Ambassador Petr Iliichev, after the council envoys met with the African Union Peace and Security Council in Addis Ababa on Monday.

South Sudan gained independence from Sudan in 2011 but slid into civil war in 2013 after Kiir sacked Machar as his vice president. The pair signed a peace deal a year ago but fighting has continued and Machar has now fled to neighboring Sudan. (Reporting by Michelle Nichols; Editing by James Dalgleish)