China has rejected an explanation by visiting US envoy Thomas Pickering that Nato's bombing of the embassy last month was a mistake.

The official Xinhua news agency quoted Chinese Foreign Minister Tang Jiaxuan as telling Mr Pickering that the US explanation was "unconvincing and unacceptable."

Three Chinese journalists were killed and more than 20 others wounded in the 7 May attack, which caused outrage in China.

Mr Pickering was sent to Beijing in an attempt by Washington to move bilateral relations beyond the embassy attack.

BBC Beijing Correspondent Duncan Hewitt: "Punishment of those responsible is a key demand."

But Mr Tang demanded that the United States make a more satisfactory explanation.

The US said the bombing was a "tragic mistake" which stemmed from the use of outdated maps, but the Chinese state media have consistently portrayed it as deliberate.

A statement issued by the US Information Service in Beijing reiterated President Clinton's promise to President Jiang Zemin that a full investigation into the incident would be conducted.

'Tragic' bombing

But the Chinese news agency also quoted Mr Pickering as saying that the US realised that no explanation could make up for the tragedy.

Xinhua quoted him as saying: "The US investigation shows that multiple factors and errors in several parts of the US Government were responsible for the tragic mistaken bombing of the Chinese embassy.

The US said out-of-date maps were responsible for the tragedy

Mr Pickering was further quoted as saying that Nato forces intended to target the headquarters of the Yugoslav Federal Directorate for Supply and Procurement.

He said that two maps produced by Yugoslavia in 1989 and 1996 and a 1997 National Imagery and Mapping Agency map were used.

None of these maps showed any indication of the location of the Chinese embassy.

Mr Pickering told the Chinese leadership that the CIA and the Defence Department were continuing to interview the individuals involved in the decision-making process that led to the bombing.

China has also demanded that those responsible be punished.

Mr Pickering, who arrived on Tuesday night with a delegation which included intelligence officials, is returning to Washington.

Nuclear secrets

Tensions between the two countries had plunged to a new low before the May attack when the US accused China of stealing its nuclear weapons technology.

Those accusations came at a critical phase as both countries were close to an agreement paving the way for China's entry to the World Trade Organisation.

China broke off talks on human rights and military co-operation, and denied American naval vessels access to Hong Kong.

Some American politicians have accused China of trying to exploit the accident for political gain.

Congress is debating whether to go along with President Clinton's decision to extend Beijing's trade status for another year.

Congress is expected to abide by that decision, but only after attacks on China for its trade practices, human rights record and threats to US security.