TEHRAN, Sept 6 (Reuters) - The head of the United Nations refugee agency called on Saturday for greater efforts to increase voluntary refugee returns to Afghanistan, which have virtually come to a halt amid a worsening security situation.

Around 4.5 million Afghans who fled their homeland during 30 years of almost continual war began returning from neighbouring Pakistan and Iran after the 2001 overthrow of the Taliban.

But Antonio Guterres, the United Nations High Commissioner for Refugees, told a news conference the number of refugees now returning was "very, very small" because living conditions in Afghanistan were again deteriorating.

"That is why it is very important to commit the Afghan government and to commit the international community to strongly invest in Afghanistan to create the conditions for these voluntary repatriations to be able to pick up again," he said.

Guterres is visiting Iran, where some 900,000 registered Afghan refugees live, and praised Iran's "generosity" in taking them in. An estimated 2 million Afghans are living in Pakistan.

Violence has surged in Afghanistan this year as the hardline Islamist Taliban have stepped up their campaign of guerrilla attacks, suicide and roadside bombs to oust the pro-Western Afghan government and drive out foreign troops.

Asked whether he believed more refugees could return to Afghanistan despite such violence, Guterres said the security situation differed in different parts of the country.

He also said the virtual halt in the return of refugees was "more linked to the economic, social conditions than to the security conditions."

The U.N. refugee agency and the Afghan government plan an international conference in Kabul in November on the return of refugees and their reintegration into society, he said.

The aim was to "push for a stronger commitment of the Afghan government and a stronger commitment of the international community in order to support the actions that are required for people to be able to go back."

Iran is also home to hundreds of thousands of Afghans who, it says, live in the country illegally. Last year Iran launched a big drive to deport them to Afghanistan, despite appeals from Kabul which has said it lacks the resources to resettle them.

Many of the Afghans living in Iran work in the construction sector or as domestic help.

Guterres said it was important to make a distinction between those who are recognised as refugees and those who came to Iran mainly for economic reasons. (Reporting by Fredrik Dahl; editing by Tim Pearce)

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