A Russian proposal to end Syria's conflict that would include early presidential elections faced opposition from both sides on Wednesday, as deep divisions remained over the fate of President Bashar Assad.

Syrian legislator Sharif Shehadeh, a member of the ruling Baath party, told The Associated Press there will be no presidential vote before Assad's latest term ends in 2021. He added that parliamentary elections are an internal Syrian affair and that it was still too early to hold them.

His comments came a day after Russia circulated a document on ending Syria's conflict that calls for drafting a new constitution within 18 months. The charter would be put to a popular referendum and then followed by an early presidential election.

Shehadeh said the proposal is not official yet.

"Regarding presidential elections there will be no talk about it. The president has a term and when it ends then we can talk about it," Shehadeh said. Assad was elected for a third seven-year term last year in an election boycotted by the opposition and panned by its Western supporters.

Prominent Syrian opposition figure Haitham al-Maleh said Russia, which began launching airstrikes in support of Assad's troops on Sept. 30, is an "occupation force" in Syria, adding that the opposition will not accept any role for Assad during the transition.

"We will not accept that the regime stays even for 24 hours. Bashar should be detained and put on trial," al-Maleh, a senior member of the Western-backed Syrian National Coalition, said by telephone from Egypt.

The Russian document, obtained Tuesday by The Associated Press, makes no mention of Assad stepping down during the transition -- a key opposition demand. It only mentions that "the president of Syria will not chair the constitutional commission."

Al-Maleh said Russia wants "the current regime to stay," adding that the Russian air campaign "will be defeated."

In New York, Britain's U.N. Ambassador Matthew Rycroft told reporters Wednesday that Britain has seen the proposal and is discussing it.

"The eight-point plan itself is not central to the discussions in Vienna but Russia is, and we want to be working very carefully and closely and continually with all of those around the Vienna table to come to agreement on how to implement the Geneva communique," Rycroft said.

He was referring to the 2012 Geneva communique agreed to by major world powers calling for a transitional government in Syria, with full executive powers, agreed to by both sides leading to elections.

The Russian document was circulated ahead of a second round of talks in Vienna on Saturday among key governments on both sides of the Syrian conflict.

Iran's Deputy Foreign Minister for Arab and African Affairs Hossein Amir-Abdollahian told the Beirut-based Al-Mayadeen TV on Wednesday that if the United States "exploits the Vienna meeting in what serves its interests then Iran will not take part in the meeting."

Iran and Russia have been Assad's strongest supporters since the conflict began in March 2011.

At the initial talks in Vienna on Oct. 30, the U.S., Russia, Iran and more than a dozen other nations agreed to launch a new peace effort involving Syria's government and opposition groups.

But they carefully avoided the issue of when Assad might leave power, a dispute at the heart of the conflict, which has claimed more than 250,000 lives and generated more than 4 million refugees.

Russian Foreign Ministry spokeswoman Maria Zakharova said Wednesday that the key subject on the agenda of the weekend talks in Vienna would be the creation of a list of the opposition that could be part of political talks and a list of "terrorists."

Asked what role Assad should play, she said it was something for the Syrian people, not Russia, to decide.