NEW YORK — Kofi Annan, the special envoy whose peace plan for ending the increasingly violent conflict in Syria is paralyzed and at risk of complete collapse, asked the UN Security Council on Wednesday to threaten the Syrian government and the rebels with consequences for failure to comply.

Annan made his request as new evidence emerged of fracturing in the government of President Bashar Assad of Syria, which has faced a slow but growing rash of defections and desertions. The latest was Syria’s ambassador to Iraq, Nawaf Fares, who issued a statement reported by Al-Jazeera and Reuters that he had resigned and had renounced his membership in Assad’s Syrian Ba’ath Party.

“I urge all honest members of this party to follow my path because the regime has turned it to an instrument to kill people and their aspiration to freedom,’’ Fares said in the statement from an unidentified location. There was no immediate comment from the Syrian government on the defection, the first by a Syrian ambassador since the uprising broke out in March 2011.

The Security Council has already passed two resolutions that request compliance with Annan’s plan but do not carry coercive pressure. ‘‘You should insist on implementation of your decisions, and send a message to all that there will be consequences for noncompliance,’’ Annan, who represents the UN and Arab League, told the Council.

Annan did not specify that the Council should threaten measures under Chapter 7 of its charter, which authorizes economic sanctions, and if necessary, military action, as was done in the Libyan conflict last year. But his request quickly laid bare the makings of a potential confrontation among the five permanent members of the Council, whose effort to speak in a unified way on the Syria conflict has often masked serious divisions.

Representatives of the United States, Britain, and France said they would address Annan’s request with a resolution that included Chapter 7 sanctions. But Russia and China, which have twice blocked such coercive measures, were expected to resist. Russia, the Syrian government’s most important foreign supporter, circulated its own draft resolution that does not include the Chapter 7 provision.

Alexander Pankin, the ranking Russian diplomat at the Security Council, said that Annan had ‘‘asked that the Council speak in a united and single voice. And there will be consequences. But consequences does not mean under a certain chapter or certain article.’’

Annan, who spoke to the Council by video link from his Geneva office after having visited Syria, Iran, and Iraq, also said that Assad was open to the idea of an interlocutor between him and the political opposition, which presumably would allow a dialogue without the two sides’ having to directly talk to each other.

It was not clear whether Syria’s array of anti-Assad groups, who have said they would not negotiate with Assad, would agree to such an idea.

Annan addressed the Council less than two weeks before authorization of the 300-member observer mission in Syria, assigned to monitor a cease-fire and other provisions of the plan, will expire. The observers, who are unarmed and have no enforcement authority, suspended work a month ago because both the Syrian government and its armed antagonists were ignoring Annan’s plan, and the rising violence had made the mission’s work too dangerous.

Both Annan and the UN secretary general, Ban Ki-moon, want the Council to renew the mission’s mandate. Ban has said a withdrawal of the mission would send the wrong signal and encourage more violence. While the Council is expected to reauthorize the monitors, the size of their group and duration of deployment remain to be negotiated.

The defection of Syria’s ambassador to Iraq was the second high-ranking exit from Assad’s government in less than a week, following the departure last Thursday of Manaf Tlass, a general in the elite Republican Guard. Fares, who received the Baghdad posting in 2008, was described at the time of his appointment as a well-connected statesman whose family was rooted partly in the Sunni tribal society of Iraq’s Anbar Province, which extends to Syria’s eastern desert.