* Ethiopia, Kenya, Sudan, Uganda report no cases for a year
* But new polio cases detected in Russia and Congo
GENEVA, July 30 (Reuters) - Eastern Africa is free of polio again, with four countries -- Ethiopia, Kenya, Sudan and Uganda -- having reported no cases of the crippling disease for more than a year, U.N. and other aid agencies said on Friday.
But the virus appears to have spread from Tajikistan, where it has paralysed 437 children since April, to infect 6 ethnic Tajiks in Russia, according to the World Health Organisation.
"It was detected in a few individuals in Russia in Tajik communities. An investigation is going on, we don't know where infection took place," WHO spokesman Oliver Rosenbauer told Reuters.
Russia's last confirmed case of polio was in 1996, but if the investigation shows the victims were infected in Tajikistan, they would be classified as part of the epidemic there, he said.
And in another setback to the elusive two-decades-old bid to wipe out polio worldwide, a single known case in the Democratic Republic of Congo may have been imported from Angola, which also has an outbreak, according to the WHO.
Aid agencies are trying to limit further international spread of polio and stop new outbreaks more rapidly. In all, there have been some 576 confirmed cases globally this year, against 1,604 in all of 2009.
Some 101 children were paralysed in the four Horn of Africa countries between March 2, 2008, and July 30, 2009, after the virus reappeared in southern Sudan and Ethiopia and began spreading.
"Today marks a step towards the achievement of a major objective of the Global Polio Eradication Initiative's new strategy -- stopping polio in Africa," said the initiative which links governments, U.N. aid agencies, Rotary International and the U.S. Centers for Disease Control and Prevention.
"All eyes will also be on Angola and Chad to end transmission by the end of 2010," it said. Angola and Chad have recorded 16 and 14 cases, respectively, this year, according to its figures.
Polio remains endemic in four countries -- Afghanistan, India, Nigeria and Pakistan.
The virus was imported from endemic areas, causing outbreaks such as those in Angola and Tajikistan, the statement said. (Reporting by Stephanie Nebehay; Editing by Jonathan Lynn)