Poland reopened its airspace at 4:00 am (0200 GMT) Sunday but only for planes overflying the country, the spokesman for the Polish air traffic control agency said. 'The cloud of volcanic ash has moved lower, which means that the sky above is becoming clear,' the spokesman, Grzegorz Hlebowicz, was quoted as saying by the PAP news agency. 'We decided to open the airspace from 4:00 am until further notice for aircraft which are flying at an altitude above 6,000 metres (19,685 feet),' he said. The announcement came after world leaders including US President Obama cancelled their attendance at the funeral of Polish president Lech Kaczynski on Sunday because of the plume of ash from an Icelandic volcano that has caused air travel chaos across Europe. 