A key witness in Pakistan's "Memogate" scandal Wednesday said he delivered a secret memo seeking American help to avert a feared coup after Islamabad's ambassador to the US told him it was from the president.

Testifying via live video link from London before a judicial commission in Islamabad probing the scandal threatening President Asif Ali Zardari, American businessman Mansoor Ijaz said he delivered the request to a US general.

The controversial unsigned memo was allegedly an attempt by Zardari, through his close aide and former envoy Hussain Haqqani, to enlist help from the US military to head off a feared coup in Pakistan last year following the killing of Osama bin Laden by US Navy SEALs.

"I asked (Haqqani) on whose authority he was doing this?" Ijaz said.

"He (Haqqani) said this is coming from the president of Pakistan who wanted to put together a new national security team similar to national security team in USA," Ijaz said.

Ijaz told the commission that he drafted the memo after Haqqani gave him points and requested that it should be delivered to Admiral Mike Mullen, then chairman of the US Joint Chiefs of Staff. The memo was delivered on May 10.

He said Haqqani called him on May 9 and said the army was contemplating a coup following the May 2 US raid which killed bin Laden in the Pakistani garrison city of Abbottabad.

"The army wants to bring this government down," Ijaz quoted Haqqani as saying.

Ijaz said Haqqani wanted him to convey this fear to Mullen and request him to ask Pakistani army chief General Ashfaq Kayani to step down.

Ijaz said Haqqani gave him points to be conveyed to Mullen which included assurances on giving the US administration the choice of selecting members of a commission to probe bin Laden's presence in Pakistan.

The Pakistani envoy also offered that if Kayani stepped down, Islamabad would assist the US "in locating other bad guys and we also commit American boots on the ground," Ijaz said.

"He (Haqqani) further offered that Pakistan would agree on an additional discipline as regard to the nuclear programme," Ijaz said.

The US and western governments have expressed fear that Pakistan's nuclear weapons might fall into the hands of militants, but Islamabad insists that its arsenal and facilities are well guarded and secured.

The commission will reconvene on Thursday and resume recording the statement from Ijaz.