Finance ministers from the Group of Eight economies have given their clearest pledge to continue to lighten the burden of debt on the world's poorest countries.

The Highly Indebted Poor Countries' Initiative, which had been due to expire at the end of this year, now looks certain to be extended. In the final communiqué at the meeting in New York, G8 finance ministers said there should be full implementation of the Hipc initiative, which has so far left behind some highly indebted countries such as Sudan.

The ministers also agreed to explore the need for additional aid to countries that still had unsustainable debt levels even after completing the Hipc process.

Gordon Brown, the UK finance minister, indicated that work was being done on the definition on debt sustainability. The current definition used by Hipc - that debt should be no greater than 150 per cent of annual exports - has been widely criticised for failing to fully reflect a country's ability to service debt.

"We have got to do more, and we will do more," said Mr Brown in New York yesterday, adding that he expected further developments over the next few weeks.

The communiqué offered an upbeat assessment of the state of the world economy, with ministers boasting that sound pro-growth policies had resulted in the strongest growth rate in 15 years. Ministers stressed the threat to the rapid recovery in the global economy from strong oil prices, but said they would continue to pursue measures to boost the potential rate of growth.

The imbalance in rates of growth in the world's leading economies was underlined by a surge in the US trade deficit to $46bn (?38bn) in April. The US has continued to harry European nations over the slow pace of structural reforms, which represents a potential drag on the potential maximum of the US growth rate.

John Taylor, the US undersecretary for international affairs, said ahead of the meeting that the ministers would need to discuss the best way to "get reform through a political system".

Ministers also discussed the need to reform the International Monetary Fund and World Bank, saying that the institutions must change further to achieve their goals of promoting stronger economic growth and poverty alleviation.

The final communiqué set out the principles of these reforms, indicating the need for a clearer separation of functions between the two institutions and a more effective relationship with financial markets.