US Secretary of State Condoleezza Rice has expressed concern at the progress of democracy and media curbs in Russia.
A bomb threat delayed Ms Rice's arrival to Moscow
"The trends have not been positive on the democracy side," Ms Rice said shortly before arriving in Moscow for her first visit as the top US diplomat.
She said the Kremlin's consolidation of power was "clearly very worrying".
But Ms Rice will not be seeking a row with President Vladimir Putin, who the US sees as an ally in its war on terror, a BBC correspondent says.
She will also be laying the ground for a visit to Russia by George W Bush next month for World War II commemorations.
The US wants Russia to help fight the spread of nuclear technology, especially in preventing Iran and North Korea from acquiring nuclear weapons, BBC state department correspondent Jonathan Beale says.
Soon after Ms Rice's arrival, a bomb threat at the hotel where she was due to be staying forced her motorcade to be diverted to the American ambassador's residence - a standard procedure in emergencies.
Russian officials later gave an "all clear" signal after sweeping Moscow's Renaissance Hotel in the city centre.
The Russian Emergency Ministry said there was no bomb, our correspondent says.
On Wednesday, Ms Rice will go to Lithuania on Wednesday for a Nato meeting - the first time the organisation's foreign ministers meet on former Soviet territory.
'Commit to democracy'
Ms Rice made her comments to reporters on board her plane shortly before landing in a Moscow airport.
She also urged President Putin to make good on his promise not to seek a third term in office.
But Ms Rice added that "one can't imagine reverting back to Soviet times".
And in a speech to US newspaper editors last week Ms Rice stressed that her message in Moscow would be "that a democratic and vibrant and prosperous Russia is in everyone's interests".
"Our relationship with Russia holds enormous potential, and we can do even more together as Russia moves along a democratic path," she said.
Ms Rice met Russian Foreign Minister Sergei Lavrov in Turkey in February during a seven-day tour of Europe after becoming secretary of state.
In that meeting, she said Russia must do more to show it is committed to democracy if it wants deeper relations with Western nations.
Media watchdog letter
That included strengthening the rule of law and permitting a free press, she said.
International media watchdog Reporters Without Borders on Monday urged Ms Rice to raise the issue of attacks on Russian journalists when she meets President Putin on Wednesday.
"Journalists in Russia are being subjected to a rising spiral of violence with numbers of them suffering brutal attacks," the organisation said in a letter to Ms Rice.
"No fewer than 17 journalists were physically attacked and three threatened in 2004 alone, because of their work."
Several reporters have also been murdered in recent years, including US journalist Paul Klebnikov who worked for the Russian edition of Forbes magazine in Moscow.
Before joining the Bush administration, Ms Rice was an academic specialising in Russia.