Suspicious packages on freighters in Dubai, UK and US

Authorities on three continents are investigating whether suspicious packages shipped from Yemen to religious sites in the US were part of a "terrorist plot".

No explosives have been found so far, but officials said they are investigating whether the packages were sent as part of a dry run for an attack.

The package in Britain, discovered aboard a jet in the East Midlands about two hours north of London, contained a toner cartridge with attached wires and powder.

It was found during routine screening of cargo, prompting authorities to search three aircraft and a lorry in the US on Friday, US officials said.

Qatar-based Al Jazeera TV reported that Yemeni authorities have denied claims that a direct cargo route from Yemen to the US exists.

"Authorities here continue to reiterate, however, that they are doing all they can to eliminate al-Qaeda from the country, amid growing international pressure," he said.

Yemeni officials said they launched a terrorism investigation and Scotland Yard said its investigators were testing a number of items seized from the jet in East Midlands.

In the US, searches were conducted in Philadelphia, Newark, New Jersey and New York City.

The packages were being sent via the shipping companies United Parcel Service (UPS) and FedEx. The packages, not the flights, originated in Yemen.

An Emirates flight from Dubai carrying another package from Yemen landed safely at Kennedy airport and was met by law-enforcement authorities. The aircraft was escorted by US fighter jets, a law-enforcement official said.

AL Jazeera quoted Mike Mangeot, a UPS spokesman, who said two jets in Philadelphia that had come from Cologne, Germany, and Paris were being investigated. "Out of an abundance of caution, those aircraft have been isolated, and they are looking into the shipments in question there," he said.

In central England, police evacuated a freight distribution building at East Midlands airport after a suspicious package was reported.