By Louis Charbonneau and Michelle Nichols

UNITED NATIONS, Nov 6 (Reuters) - The U.N. political affairs chief told the Security Council on Tuesday of credible reports that the Syrian government is using cluster bombs and diplomats said peace mediator Lakhdar Brahimi had urged Russia to be more "pro-active" in ending the war.

Jeffrey Feltman, the U.N. undersecretary general for political affairs, made the remarks at a closed-door session of the 15-nation Security Council on Syria, envoys said.

Brahami had also told urged Russia at the weekend to do more to help end the war, they said.

"In his meeting with (Foreign Minister Sergei) Lavrov, Brahimi encouraged Russia to take a more 'pro-active' role in resolving the Syria crisis," a diplomat told Reuters on condition of anonymity.

Feltman confirmed to reporters after the meeting that he had informed the council about "credible reports of the use of cluster bombs by the government." He added that reported atrocities by rebels were also a serious concern.

Cluster bombs are banned under a 2010 treaty, though Syria, like Israel, Russia, the United States and other producers or alleged users of cluster bombs are not parties to the pact.

Russian U.N. Ambassador Vitaly Churkin declined to comment to reporters when asked about Feltman's comments.

Russia has accused Western powers of preparing a Libya-style military intervention in Syria that would lead to the ouster of Syrian President Bashar al-Assad, who is Moscow's ally and a top buyer of Russian arms. It has vowed to prevent that.

Some 32,000 people have died in Syria's conflict.

British Ambassador Mark Lyall Grant told reporters he hoped Brahimi would present the council with a plan for Syria before the end of the month.

"We hope that Mr Brahimi will come with some ideas and some recommendations for council action," he said. "We believe it's long past the time when the council needs to take stronger action than the few statements and ... resolutions that we have so far adopted on Syria."

Brahimi said on Sunday he hoped the Security Council would issue a resolution based on a deal they reached in June to set up a transitional government in a bid to end the bloodshed.

Speaking at the same Cairo news conference, however, Lavrov dismissed the need for a resolution, saying others were stoking violence by backing rebels - comments that highlighted the deep impasse over Syria's civil war.


DEADLOCK

Reporters asked Lyall Grant about Brahimi's call on Russia to be more pro-active in helping to end the conflict.

"I think he's hoping everyone will be more proactive," he said. "But clearly the fact that Russia and China have three times vetoed efforts by the Council to take more coercive action against the regime, there is a particular responsibility on them."

"They are supporting the Assad regime and therefore they have a particular responsibility as permanent members of the council to stop this violence," Lyall Grant added.

The Syrian government and a number of opposition groups had accepted Brahimi's proposal to hold their fire for the Islamic holiday of Eid al-Adha Oct. 26-29 but there was hardly any lull in the fighting.

"The question of who violated the truce first is therefore not the key question," a diplomat said, quoting Feltman. "The main issue is that despite interest on both sides to silence guns, the parties remain locked in their fears and mistrust."

Feltman did, however, suggest that jihadists were to blame for sparking violence during the ceasefire, a diplomat said.

Overall, Feltman said that since Friday violence has returned to pre-Oct. 26 levels and has in fact escalated in the north. He also said Oct. 30 was the first time that Syrian government fighter jets struck the Damascus suburbs. The military had previously used helicopters.

The Security Council has been deadlocked for more than a year on Syria. Russia and China have vetoed three resolutions condemning the Syrian government and have ruled out the idea of sanctioning Assad's government.

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  • This photo released by the Syrian official news agency SANA, shows a Syrian man helping an injured man at the scene after a blast occurred according to footage and reports shown on State-run Al-Ikhbariya television in the Mazzeh al-Jabal district of the Syrian capital Damascus, Syria, Monday, Nov. 5, 2012. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrians standing at the scene after a blast occurred according to footage and reports shown on State-run Al-Ikhbariya television in the Mazzeh al-Jabal district of the Syrian capital Damascus, Syria, Monday, Nov. 5, 2012. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrians pushing a burnt car at the scene after a blast occurred according to footage and reports shown on State-run Al-Ikhbariya television in the Mazzeh al-Jabal district of the Syrian capital Damascus, Syria, Monday, Nov. 5, 2012. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrians standing at the scene after a blast occurred according to footage and reports shown on State-run Al-Ikhbariya television in the Mazzeh al-Jabal district of the Syrian capital Damascus, Syria, Monday, Nov. 5, 2012. (AP Photo/SANA)

  • This photo released by the Syrian official news agency SANA, shows Syrians standing at the scene after a blast occurred according to footage and reports shown on State-run Al-Ikhbariya television in the Mazzeh al-Jabal district of the Syrian capital Damascus, Syria, Monday, Nov. 5, 2012. (AP Photo/SANA)