Washington/London, Oct 30 (DPA) A global terrorism scare was triggered Friday when a series of suspicious packages were investigated on cargo flights to US destinations at airports in the US, Britain and Dubai.

The flights had originated from Yemen and were described as a "potential terrorist threat" by White House spokesman Robert Gibbs, though it appeared that no actual explosives had been found in the devices.

One package was discovered early Friday on a flight bound for Chicago while it was on a stopover at East Midlands airport, near Nottingham in central England. There was never a threat to Britain itself, Scotland Yard said.

The device on a plane operated by packaging firm UPS was described by police as a "manipulated toner cartridge", but tests for explosives had come back "negative".

Another suspicious package was discovered on a flight operated by packaging firm FedEx and confiscated at their facility in Dubai. FedEx said it was halting all flights out of Yemen as a result of the threat.

Gibbs said intelligence received late Thursday night had led investigators to inspect the flights, which both originated in Yemen and been destined for the US. President Barack Obama was also receiving regular updates.

Yemen has become a hub for terrorist groups including Al Qaeda in the Arabian Penninsula, which has been linked to numerous plots. The group claimed responsibility for the failed plot to bomb a Detroit-bound airliner Dec 25, 2009.

Two other UPS cargo planes were isolated and checked for suspicious items at a US airport in Philadelphia and one plane in Newark, New Jersey, though both airports were later given the all-clear.

US officials said there had been no specific bomb threats at the airports, but that the planes were checked "out of an abundance of caution". Security and cargo screening was also stepped up at other US airports, the Department of Homeland Security said.

The cordon around the cargo distribution centre at East Midlands airport had also since been lifted and "police have gone home", police in nearby Leicester said.

US broadcaster CNN reported the searches of cargo flights were the result of "specific intelligence" and that one of the packages was addressed to a Jewish synagogue in Chicago.

The US Anti-Defamation League in a statement said it had alerted Jewish communal institutions across the US to increase their mailroom security as a result of the threat.

The alerts also triggered other scares. There were reports of a UPS truck being stopped in the New York City borough of Queens and other suspicious devices being investigated in Britain.

UPS in a statement said it was "fully cooperating" in the investigations with authorities.

US media originally reported the scare as having been on a plane in London. But the British Airport Authority (BAA), which operates most of Britain's airports, said no suspicious devices had been found at major London airports.