Iran's foreign minister said yesterday that Tehran would be "co-operative" in response to changes in US policy, following the revelation that President Barack Obama's team is drafting a landmark letter to the Islamic Republic aimed at thawing a three-decade freeze in relations.

Manouchehr Mottaki, speaking at the World Economic Forum in Davos, hedged his response by saying that Obama would have to change Washington's policy in the Middle East, "not in saying but in practice". If that happened, he said, the new administration would definitely find "a cooperative approach and reaction" from the region, and from Iran in particular.

The remarks followed the Guardian's report on Thursday that Obama was formulating a conciliatory letter to Iran's leadership aimed at unfreezing relations between Washington and Tehran and clearing the way for direct talks for the first time since the 1979 Islamic revolution.

There were more hostile noises from other sections of Tehran's disparate government, suggesting that the US overtures had caused disarray. Ayatollah Ahmad Jannati, chairman of the influential Council of Guardians and an outspoken supporter of President Mahmoud Ahmadinejad, warned against rapprochement yesterday and denounced supporters of the idea as "troublemakers" from "hated groups".

Diplomats in London and Washington stressed that no decisions on future steps were likely to be taken by Washington before the end of a month-long policy review, which began after Obama's inauguration on 20 January. However, there will be important meetings next week aimed at ensuring that the US remains in step with its negotiating partners.

Political directors from the foreign ministries of the six countries negotiating with Iran - the US, Britain, France, Germany, Russia and China - will meet in Frankfurt on Wednesday to discuss the new administration's policy and attempt to arrive at a common position on Tehran's nuclear programme. The Iran issue will also be discussed at a meeting of G8 political directors in Venice at the start of next week. Those meetings could lead to a meeting of foreign ministers in February or March to declare a new common policy.

US and British diplomats say they will be looking for signs of willingness from Russia to back further isolation of Iran if Ahmadinejad rejects the olive branch offered by Obama and continues to enrich uranium. Moscow's resistance led to the collapse of a common stand on sanctions last year.

A Russian official said Moscow was prepared to back a tough position towards Iran if no new unilateral sanctions were imposed by the US or EU in the run-up to any direct talks, and if any future sanctions were solely focused on the nuclear programme. The Bush administration attempted last year to widen sanctions to target Iran's revolutionary guards for their backing of Hamas and Hezbollah.

Jannati's outburst illustrates the bitter divisions a US attempt at conciliation would sow within Iran's theocratic ruling system. It bears out warnings from some that a US gesture is unlikely to result in an immediate transformation in relations.