Pam O'Toole BBC regional analyst

The United Nations High Commissioner for Refugees, Ruud Lubbers, is in Afghanistan to review the progress of refugee return programmes there and seek ways of improving security for returnees.

Lubbers will be addressing the issue of security

UNHCR says around 1.5 million Afghan refugees have returned home from Pakistan and Iran under voluntary return programmes launched by the agency in the spring - hundreds of thousands of others have gone home under their own steam.

Meanwhile, countries like Australia and Britain are launching their own programmes to encourage tens of thousands of Afghan asylum seekers to volunteer to go home.

But some refugee groups have expressed concern about the conditions facing returnees.

Conditions 'not ideal'

In some ways the Afghan return programme has been an unprecedented success.

The number of refugees going home has far outstripped the number estimated after the fall of the Taleban.

UNHCR says this is now the largest return movement since 1971 when two million people were resettled in Pakistan.

But the conditions refugees are returning to are far from ideal. In some areas there is still fighting or human rights problems, unemployment is high, there is a lack of affordable housing.

UN reminder

The head of Afghanistan's transitional government, Hamid Karzai, has said he would like all Afghan refugees to return before elections are held in two years' time.

The conditions refugees are returning to are far from ideal

But that would mean providing assistance for a further two million people.

Mr Lubbers will talking to Mr Karzai and UN officials in Kabul on how to meet this challenge.

And he will be visiting camps for refugees and displaced people to see conditions for himself.

He will report back to donors next month - stressing that Afghan returnees need long term support to help them reintegrate and ensure they don't flee the country again.

He told the BBC that another main purpose of his trip would be addressing the tricky issue of security, particularly in the north, where there have been allegations of human rights abuses against ethnic Pashtuns.

Mr Lubbers will be reminding government officials and local commanders that to expand its assistance to Afghanistan, the UN requires security on the ground - and that everyone has something to gain by boosting security for all of Afghanistan's ethnic groups.