The UN Special Envoy to Syria Staffan de Mistura has been criticised by an ex-adviser for "the total absence of preparatory work" before announcement of his plan for securing a ceasefire in Aleppo that "is now dead".

Mouin Rabbani, De Mistura's former principal political adviser, told Al Jazeera that the envoy, who two months ago briefed the UN Security Council about the imminent start of his arrangement with the Syrian government for the freeze of air raids on the city, "simply wasn't up to the task".

In February, De Mistura said that President Bashar al-Assad's regime had shown a willingness to suspend aerial bombardment of Aleppo for six weeks to allow for a humanitarian ceasefire.

Under the plan, rebels would be asked to suspend rocket and mortar fire there during the freeze. 

A group of Syrian opposition forces rejected De Mistura's proposal, saying they would not accept a deal that involved "a person who destroyed our country," referring to Assad.

The rebels also questioned why a truce would be limited to Aleppo and not include the whole country.

"That plan is now dead," Rabbani told Al Jazeera in an exclusive interview.

'Cronyism'

De Mistura, who was preceeded by former Secretary-General Kofi Annan and veteran diplomat Lakhdar Brahimi, "simply does not have the right background and expertise," said Rabbani.

Discussing the running of De Mistura's office, Rabbani said "there was a very serious issue of - to put it bluntly - cronyism and dodgy personnel decisions".

Responding to the criticism, Stephane Dujarric, spokesman for UN Secretary-General, said the UN had "full confidence" in De Mistura and "his great team that he has put together".

"Mr De Mistura has 30 years of frontline experience in the UN's political and humanitarian work in the most dangerous places and we of course have full confidence in his work," said Dujarric.

Dujarric said prior to briefing the Security Council and the announcement of the plan, De Mistura had been in Damascus and had extensive consultations and discussions with the Syrian government.

According to Dujarric, De Mistura and his team had also been in contact with various Syrian opposition groups.

"So to say that there were no prep work is a mischaracterisation," said Dujarric.

Source: Al Jazeera