Moscow - When Russia attacked Georgia this month, Moscow could say simply it was protecting its citizens - but how did so many people in a neighbouring country come to hold Russian passports?

"I am obliged to protect the lives and dignity of Russian citizens, no matter where they are located," said President Dmitry Medvedev the day Russian troops went to repel a Georgian attempt at recapturing the separatist region of South Ossetia.

Moscow began handing citizenship years ago to residents of South Ossetia and another separatist region, Abkhazia.

Russia says this was part of a legal process. Critics say that Moscow sought to weaken Georgia's sovereignty.

Before 2002, Russian law let residents of ex-Soviet republics apply for citizenship if they had not become citizens of their newly independent states.

But the process was complex and involved repeated trips to Russian consulates or moving to Russia altogether.

Yevgeny Volk, a political analyst with the US-based Heritage Foundation think tank, says people in Abkhazia and South Ossetia got passports without the usual "colossal problems".

"This undoubtedly indicates a double standard in Russian policy and a determined effort to weaken the (separatist regions') ties with Georgia," Volk said.

Supporters of Moscow's policy say the open doors approach was justified because the separatist governments in Abkhazia and South Ossetia could not issue valid travel documents or give state benefits, like pensions.

"Since Russia is the legal heir of the Soviet Union, it is obliged to give these people its citizenship," Andrei Vashchenko, a Caucasus expert, said.

"People had a right to choose. Some got Georgian passports, but the larger part of the population got Russian ones," he said.

Vashchenko helped Russian lawmakers prepare a 2002 bill on easing citizenship applications from the two regions.

The bill set off a flood of applications in Abkhazia, where some 150 000 residents became Russian citizens in June of that year alone, according to media reports.

They joined a significant part of the province's population that already had Russian citizenship, estimated at 50 000.

Many people in Abkhazia could even apply without leaving home.

The Congress of Russian Communities, a nationalist non-governmental organisation with close ties to Russian officialdom, simply took their papers to the nearby Russian city of Sochi for processing.

A similar process unfolded in South Ossetia.

Georgia's foreign ministry decried an "unprecedented illegal campaign" and then-president Eduard Shevardnadze claimed there had been "covert annexation and violation of Georgia's sovereignty".

By the time pro-Western reformer Mikheil Saakashvili became Georgia's president after the 2004 "Rose Revolution", most residents of the two separatist zones were Russian citizens.

Russia's passport campaign led to many cases of "sham" citizenship, casting doubt on Moscow's rationale for attacking Georgia, said Christopher Waters, a law professor and Eastern Europe expert at the University of Windsor in Canada.

"Given the sham-like nature of the granting of passports in so many cases, Russia's basing its forceful actions on protection of nationals abroad... is invalid," Waters said in a written answer to questions.

Whether or not Russia sought an excuse to charge into Georgia, the passport policy may have made conflict more likely.

"I doubt very much that this policy was started" to provide a pretext for war with Georgia over the separatist regions, Fyodor Lukyanov, editor of the journal Russia in Global Affairs, said.

But once Georgia attacked, Lukyanov said, "Russia was undoubtedly bound to defend them".