Saudi Arabia will be one of the participants in the Syria peace conference planned for next month, but the United States is blocking Iran's participation, United Nations officials said on Friday. The Syrian opposition is also opposed to Iran's involvement.

Thirty countries have been invited to participate in the conference, which is scheduled to start with a meeting of foreign ministers from world and regional powers on January 22 in the Swiss city of Montreux. The actual negotiations between Syrian President Bashar Assad's government and opposition representatives will begin on January 24 at the UN's European headquarters in Geneva.

The Syrian opposition, one of the key players, still has not agreed who will represent it in the negotiations, said Lakhdar Brahimi, the UN and Arab League envoy for Syria. "What we need is a credible delegation," Brahimi said. The divisions among the rebel groups and the political opposition groups have been a long-standing problem, he added.

Brahimi's comments came after a day of meetings on Friday with the five permanent members of the U.N. Security Council — Britain, China, France, Russia and the U.S. — and Syria's neighbors Turkey, Jordan, Lebanon and Iraq.

Along with those nations, other invitees include Algeria, Brazil, Egypt, Kuwait, Oman, Qatar and the United Arab Emirates.

"Our partners in the United States are still not convinced that Iran's participation would be the right thing to do," Brahimi told a news conference. "We have agreed that we will be talking a little bit more to see if we can come to an agreement on this question."

Brahimi and Iranian Foreign Minister Mohammad Javad Zarif discussed the issue by telephone on Saturday, the Iranian Foreign Ministry reported. No details of the conversation were provided.

Disputes over who should represent the Syrian opposition and government, and whether Iran, Saudi Arabia and other regional powers should be at the table, have blocked previous attempts to bring Syria's warring sides for peace talks.

Although the Syrian National Coalition, the umbrella opposition group, has said it would attend the talks, it would not have a list of delegates ready by the end of next week, as planned, Brahimi said.

Spanish Prime Minister Mariano Rajoy said in Brussels that his country will invite Syrian opposition representatives to a meeting on January 9 in the southern city of Cordoba with the aim of "facilitating dialogue" ahead of the Swiss peace talks.

Brahimi said the Syrian government has told the UN that it has formed a delegation, which it plans to make public in the coming days.

The U.S. has been blocking the participation of Iran, a Syrian ally, pending a public statement by Tehran that it backs the official aim of the peace talks, namely a political transition in Syria. Brahimi said the Iranian government told the UN that "they support this process and they would like to work with us."

He urged both sides of the conflict to take goodwill steps ahead of the peace talks, such as releasing detained children, women, older people and Christian clergy and letting through humanitarian deliveries.

Since the civil war began in Syria in 2011, more than 130,000 people are estimated to have died while 8.8 million Syrians have become refugees inside Syria or fled to neighboring countries, according to UN statistics.

The Red Cross said it was alarmed by the number of civilian deaths reported in the northern province of Aleppo in recent days because of systematic airstrikes by the government on rebel-held areas.

"Over 100 civilians have been killed in markets, a bus station and elsewhere in densely populated areas," said Magne Barth, delegation chief of the International Committee of the Red Cross in Syria.

Local hospitals have been overwhelmed by the influx of casualties since Sunday, the committee said.

Syrian warplanes pounded several rebel-held villages in Aleppo province for a sixth-consecutive day Friday, activists and a monitoring group said.

