TIMELINE: Georgia and Russia's worsening relations

(Reuters) - Russia said on Friday its troops were responding to a Georgian assault to re-take the breakaway region of South Ossetia, and Georgia's pro-Western President Mikheil Saakashvili said the two countries were at war.

The issue of South Ossetia's independence has bedeviled Georgia's relations with Russia. Here is a short chronology of recent events:

April 3, 2008 - NATO member states at a summit in Bucharest agree that Georgia and Ukraine can one day join the alliance. They stop short of giving them a firm timetable for accession.

April 16 - Russian President Vladimir Putin orders officials to establish semi-official ties with separatist administrations in Georgia's Abkhazia and South Ossetia. Georgia says the order is a violation of international law.

April 20 - Georgia says a Russian Mig-29 fighter jet shot down a Georgian drone flying over Abkhazia. Russia denies involvement. A United Nations report will later back Georgian version of events.

April 21 - Georgia accuses Russia of shooting down the drone in an "act of international aggression". Moscow says Georgia was deliberately fanning tensions.

April 29 - Russia despatches extra troops to Abkhazia to counter what it says are Georgian plans for an attack. The next day NATO accuses Moscow of stoking tensions with Georgia.

May 4 - Separatists in Abkhazia say they shot down two Georgian spy drones over the territory they control. Georgia denies any such flights.

May 6 - Georgia says Russia's deployment of extra troops in Abkhazia has brought the prospect of war "very close".

May 30 - Georgia says it stopped flights by unpiloted spy planes over Abkhazia but reserves the right to resume them.

May 31 - Putin, now prime minister, says he backs a Georgian proposal for Abkhazia's autonomy but not full independence.

July 5 - Russian President Dmitry Medvedev urges Georgian President Mikheil Saakashvili to refrain from "stoking tensions" in Georgia's breakaway regions.

July 8 - Russian fighter jets fly into Georgian airspace over South Ossetia. Moscow says the mission was intended to "cool hot heads in Tbilisi." Two days later Georgia recalls its ambassador from Moscow in protest.

August 4 - Russia accuses Georgia of using excessive force in South Ossetia after the Russian-backed rebels said Georgian artillery had killed at least six people.

August 7 - The head of Russian peacekeepers in the region is quoted as saying Georgia and South Ossetian separatists agreed on a truce until they hold Russian-mediated talks.

-- Russia later says Georgia's military operation in South Ossetia shows Tbilisi cannot be trusted and NATO should reconsider its plans to admit Georgia.

August 8 - Russia sends forces into Georgia to repel a Georgian assault on South Ossetia. Russian Foreign Minister Sergei Lavrov accuses Georgia of driving people from their homes.

-- Medvedev vows to defend Russian "compatriots" in South Ossetia, where most people have been given Russian passports.

-- Russia says it will cut air links with Georgia from midnight.