Israel is still maintaining official silence a week after Syria complained that Israeli aircraft invaded its airspace in a mysterious incident which raised tensions and triggered a welter of US media speculation about possible targets for the operation.

Explanations - for what anonymous US officials have said was a strike inside Syria - range from suggesting it was aimed at the shipment of weapons to Hizbollah from Iran, to saying Syria may be building a nuclear facility with North Korean help.

Syria, which has asked for a formal complaint to be "circulated" to the UN Security Council, said last week that Israeli aircraft unloaded ammunition after being spotted and fired on by its air defences but inflicted no damage.

Reuters, The New York Times and CNN have all quoted officials - mainly in the US - as saying that Israel carried out a strike in Syria. Reuters quoted an unnamed US official on Wednesday as saying: "The strike I can confirm. The target I can't." The agency quoted another US official as saying that reports on the targets were "confused".

Meanwhile, The Washington Post reported this week a US official as saying that recent satellite imagery, mainly provided by Israel, suggested that Syria may building some form of nuclear facility with the help of material unloaded by North Korea.

The US Secretary of State, Condoleezza Rice, did little to discourage such speculation when she told Fox News this week in response to a question about possible nuclear developments in Syria that her government is working to prevent "the world's most dangerous people from having the world's most dangerous weapons".

The only hint - if such it was - dropped by an unusually taciturn Israel was the release of a video by the Israeli military shortly after the incident showing a broadly smiling Chief of Staff, Gabi Ashkenazy, shaking the hands of his deputy while sharing a Jewish New Year toast. This has helped to fuel speculation that Israel had conducted a successful mission in Syria.

Syria has not fought an outright war with Israel since 1973 when it briefly overran and was then repulsed from the Golan Heights, sovereign Syrian territory captured by Israel in the Six Day War six years earlier. Syria has long agitated for return of the Golan while Israel blames Damascus for its succour to Hizbollah and militant Palestinian factions like Hamas and Islamic Jihad.

There have been persistent reports over the last year that the US has discouraged Israel from responding to oblique overtures from the Syrian President Bashar al-Assad for a negotiated recovery of the Golan. The New York Times quoted equally anonymous US sources on Wednesday as saying that the likely targets were weapons shipments Israel believed Iran was sending to Hizbollah through Syria. That claim was dismissed later in the day by Bashar Ja'afari, the Syrian ambassador to the United Nations.

"This is blah blah," Mr Ja'afari said. "This is nonsense, this is an unfounded statement. It is not up to the Israelis or anyone else to assess what we have in Syria. There was no target, they dropped their munitions. They were running away after they were confronted by our air defence."

European diplomats who met with the Syrian Vice-President, Walid Moallem, reportedly formed the impression that Syria was not planning a military retaliation. But the Syrian Deputy Foreign Minister, Faysal Mekdad, warned after a meeting with his Russian counterpart yesterday that growing tension could yet spark violence in the region and that Syria has the "means to respond in ways that will preserve its position of power".