Stephen Dalziel BBC's Russian affairs correspondent

The Iranian Foreign Minister, Kamal Kharazi arrives in Moscow on Thursday.

The visit has been delayed for nearly two months, largely because of Russian uncertainty as to how it might affect Moscow's relationship with Washington.

Russia is uncertain how the visit will go down in Washington

The Americans have cited Iran as a potential enemy, which is seeking to develop weapons of mass destruction.

But Russia sees Iran as a trade partner.

By welcoming Mr Kharazi to Moscow, the Russian President, Vladimir Putin, is walking a diplomatic tightrope.

Nuclear power

Ever since the attacks on the United States last September, Mr Putin has been keen to show that Moscow stands alongside Washington in the fight against international terrorism.

The Russian president has even had to face up to the accusations of some members of his parliament that Russia is conducting a pro-American foreign policy.

Mr Putin has been keen to show that Moscow stands alongside Washington in the fight against international terrorism.

The postponement of Mr Kharazi's visit in February was cited as an example of this.

Washington ranks Iran alongside Iraq and North Korea as its potential main enemies.

But Russia has been helping Iran construct a nuclear power plant, and appears determined to continue with the project.

The plant is scheduled to be completed in 2004.

Greatest challenge

Russian arms manufacturers also see Tehran as a potentially valuable customer, and will be keen to discuss with Mr Kharazi ways of extending cooperation.

So Mr Putin must try to balance the interests of his own nuclear power sector and arms industry, while convincing the US that these actions will not harm American interests, nor, more importantly, work against the struggle with international terrorism.

So far, Mr Putin has managed to come out of all of his foreign policy adventures with his international reputation enhanced.

Squaring the circle of Iran, the US and his own domestic interests may be his greatest challenge yet.