A British airport is at the centre of an international terrorism alert after the discovery of suspicious packages on cargo flights destined for the US.

An area of East Midlands airport – Britain's largest air freight terminal – was sealed off after investigators found a package containing a toner cartridge on a United Parcel Service plane from Yemen to Chicago.

Other planes in the United States were placed under investigation, and Federal Express said a second suspicious package had been found in Dubai on a plane originating in Yemen. FedEx and UPS have suspended cargo flights from Yemen.

US officials say the intelligence services have recently tracked three other packages from Yemen for delivery to the US that appear to be trial runs for the smuggling of a bomb on board a cargo plane. It is thought that synagogues in Chicago were among the targets.

The Associated Press reported that the cartridge found in the UK had been manipulated, and that officials found wires attached to it. They were also reported to have found a quantity of white powder.

Initial tests for explosives proved negative, but concerns remained that the nature of the package meant it could be a test run for a bomb. The FBI immediately ordered a search of other UPS planes arriving in the US, including another flight via East Midlands airport.

Images of the toner cartridge with wires hanging out of it. Photograph: Universal News And Sport (Europe)

Nothing was found on that plane, at Newark, in New Jersey, and it was allowed to proceed to UPS's main base in Louisville, Kentucky.

Two other cargo flights, via Paris and Cologne, were grounded at Philadelphia and a bomb squad was called out to search a UPS cargo lorry in New York.

The US transportation and security administration said authorities were acting "out of an abundance of caution". It said: "The planes were moved to a remote location where they are being met by law enforcement officials and swept."

In Brooklyn, New York, police were examining a package from a UPS truck after reports that a possible explosive had been found.

Police in the UK said East Midlands airport, near Nottingham, was continuing to operate.

Earlier, CNN said earlier reported that a plane had been stopped in London. The Department for Transport said it was unaware of any incident in London, but knew about the East Midlands incident.

Police evacuated a distribution centre at the airport after the package was discovered in the early hours of this morning. Officers announced that there was no threat shortly before 10am, but put cordons back up again at about 2pm.

In a statement Leicestershire police said: "At 3.28am this morning police dealt with a report of a suspicious package within a distribution centre at East Midlands airport. Police and emergency services have been dealing with the incident. The package is being re-examined as a precaution and as such the cordons that were originally put in place have been reinstated as a precaution."

It said the airport continues to operate as normal. The airport distribution centre is used by a number of companies, including UPS, Royal Mail and DHL.

The Jewish Federation of Metropolitan Chicago said: "We were notified this morning that synagogues should be on alert and we are taking appropriate precautions and are advising local synagogues to do likewise."

A White House spokesman said Barack Obama had been informed of the security operation and potential terror threat. He said: "Last night, intelligence and law enforcement agencies discovered potential suspicious packages on two planes in transit to the United States. Based on close co-operation among US government agencies and with our foreign allies and partners, authorities were able to identify and examine two suspicious packages.

"Both of these packages originated from Yemen. As a result of security precautions triggered by this threat, the additional measures were taken regarding the flights at Newark Liberty and Philadelphia International Airports."

Yemen has been trying to quell a resurgent branch of al-Qaida, which has stepped up attacks on western and government targets in the Arabian peninsula country.

US officials say intelligence agencies have over recent months tracked three other packages out of Yemen for delivery to the US that appear to be trial runs for the smuggling of a bomb on board a cargo plane. They say that the grounding of planes from the US and UK to Dubai for further searches is in part based on that intelligence.

Their suspicion is that al-Qaida in the Arabian peninsula, which was responsible for the failed attempt to blow up a passenger aircraft over Detroit on Christmas day using a Nigerian suicide bomber, is planning an attack on cargo planes.