At talks in Washington, Secretary of State Madeleine Albright told the Russian Interior Minister Vladimir Rushaylo, that she could not see how the two sides could reach a negotiated political solution to the conflict based on Moscow's current strategy.

Her spokesman said that, during the hour-long meeting, she made crystal clear her concern about the direction the Russian military campaign was taking.

The BBC's Flora Botsford: "They meet little resistance"

The United States recognises Moscow's right to combat internal security threats but has repeatedly criticised the humanitarian impact of the current operation.

Officials have also expressed concern about reports of widespread Russian intimidation of Chechens and other groups throughout the Caucusus region.

Mr Rushaylo, for his part, gave the American Secretary of State what he said was hard evidence of Chechen terrorism.

Convoy attack

About 200,000 Chechen refugees have fled in the face of the Russian onslaught to neighbouring republics.

Mrs Albright disapproves of Moscow's strategy

Latest reports - denied by Moscow - say that a Russian rocket attack on a convoy of Chechen refugees killed about 50 people and injured dozens more.

Eyewitnesses said a Russian plane fired a missile at a column of cars and buses near the border with Ingushetia.

The refugees had gathered after reports that the Russians would open the border to allow them to leave.

BBC News' Orla Guerin: Russia warning that Chechnya is an internal matter

Russian troops allowed some wounded people to cross into Ingushetia, where they spoke to journalists. Many more refugees have been turned back.

Reuters correspondent Maria Eismont spoke to eyewitnesses. She said: "I heard Chechens saying about 50 were killed, but I can't confirm that number and neither could these people I have talked with.

'Terrorists targeted'

Russian officials continue to insist their forces are striking only at terrorist bases.

Reuters correspondent Maria Eismont in Ingushetia

But Chechen doctors working for the international humanitarian organisation, Medicines du Monde, say that is not true.

A Moscow-based spokesman for the organisation said: "There are a lot of civilian victims, dead and injured people. They are bombing hospitals, schools, markets, houses. One can witness it every day."

BBC Moscow correspondent Andrew Harding says there is now overwhelming evidence that Russia's massive air bombardment is causing heavy civilian casualties.

The BBC's Richard Lister: "Mrs Albright made crystal clear her concern"

Russia unleashed a new wave of air strikes on Friday, bombing Chechnya's capital Grozny and its second-largest city Gudermes, which troops are trying to seal off.

Russian officials say they are at least half-way towards surrounding the capital Grozny and hope to encircle it completely by the end of the month.

Militants in Chechnya have in the past launched violent raids on neighbouring regions and have been blamed by many for the recent bomb attacks in Moscow and elsewhere.

Kofi Annan: The solution must be political

Chechnya's spokesman in Europe, Salih Brandt, said the war was effectively being financed by the international community.

"It's the IMF money, the British money, the American money, the German money which is propping up the Russian economy.

"And that's all going into the Russian war machine and killing these people."

UN mission

The United Nations has meanwhile announced plans to send a team of humanitarian experts to parts of Russia bordering Chechnya to assess the needs of thousands of people who have fled the fighting.

The team is to leave within days and is expected to go to Ingushetia and Dagestan, where almost 200,000 Chechens have taken refuge.

UN Secretary-General, Kofi Annan, has also sent a senior official to Moscow to discuss sending a UN humanitarian mission to Chechnya.

Mr Annan appealed to both sides to show restraint and take special care to avoid civilian casualties.