FBI agent Robert Hanssen's arrest started the row

The US immediately ordered out four Russian diplomats and 46 others were told to leave by 1 July.

The Russian Government retaliated one for one.

It was the worst Moscow-Washington spy row since the end of the Cold War.

FBI agent Robert Hanssen, whose arrest sparked the crisis, is accused of spying for the Soviet Union and Russia for at least 15 years in exchange for payments of cash and diamonds.

He is alleged to have exposed a number of Russians recruits during the Soviet era, some of whom were executed.

Many of the charges against Mr Hanssen carry the death penalty.

But the US Justice Department is reported to have agreed in principle that he will not face execution but be sentenced to life without parole if he reveals all and pleads guilty.

A provisional trial date has been set for October.

FBI review

In the wake of the crisis, the United States Attorney-General announced a comprehensive review of the FBI, which had failed to spot Mr Hanssen within its own ranks for many years.

The spy row came just a few weeks into George Bush's presidency and marked a distinct cooling of relations with Moscow.

However the atmosphere has improved since the successful summit in June between Mr Bush and Russian President Vladimir Putin.