* Syria mediator Brahimi determined to quit, diplomats say
* U.N. Security Council deadlocked over how to act on Syria
* Syria blocking access to U.N. chemical weapons inquiry
U.N. chief Ban Ki-moon and ambassadors from the United States, Britain, France, Russia and China discussed on Thursday "possible diplomatic moves to end" the Syria conflict after U.N. diplomats said mediator Lakhdar Brahimi was determined to quit.
Diplomats, speaking on the condition of anonymity, said on Wednesday that Brahimi wanted to resign from the joint U.N.-Arab League role because he is frustrated with international deadlock over how to end Syria's two-year war that has killed 70,000.
The envoys from the permanent five veto-wielding members of the U.N. Security Council declined to comment after meeting with the secretary-general. A dispute between Russia and the United States over Syria has left the council paralyzed.
Brahimi, appointed last year after former U.N. Secretary-General Kofi Annan resigned as Syria mediator, also wants to distance himself from the Arab League, envoys said, because of its decision to recognize Syria's opposition.
Brahimi felt that move undermined his neutrality. He could quit the joint mediator role and possibly be reappointed as an U.N. adviser to Ban an Syria, diplomats said.
Ban's spokesman Martin Nesirky said of Ban's meeting with the council envoys: "(They) discussed possible diplomatic moves to end the crisis. He briefed them on the latest developments relating to the chemical weapons investigation mission."
Syria has blocked unfettered access by the U.N. mission, which was created by Ban nearly six weeks ago and has an advance team in Cyprus ready to deploy to Syria. Diplomats say it is unlikely it will gain access any time soon.
The Syrian government and the opposition blame each other for alleged chemical weapons attacks in Aleppo in March and Homs in December. Ban wants the inquiry to look at both incidents, but Syria only wants the U.N. to probe the Aleppo attack.
U.S. President Barack Obama on Tuesday said that there was evidence that chemical weapons had been used in Syria, but that it was not yet known how the chemical weapons were used, when they were used and who used them.
Obama has warned Syria's government that the use of chemical weapons could trigger unspecified consequences. He told a news conference on Tuesday that he had asked the U.S. military to prepare options on Syria, but declined to give further details.
Forces loyal to President Bashar al-Assad retook a central district in the city of Homs on Thursday, driving a wedge between two isolated pockets of rebel resistance in Syria's third largest city, fighters and activists said.
Nesirky said Ban and the permanent five Security Council envoys also discussed on Thursday "the ever-worsening humanitarian situation inside Syria and the neighboring countries, and international efforts to alleviate it."
Five million people have fled their homes, including 1.4 million refugees in nearby countries, the United Nations says.