Afghan opium industry

Afghanistan is one of the world's largest producers of opium.

Mr Hassan said another 20,000 to 25,000 refugees were stranded on the Pakistan side of the border by protesters blocking roads in tribal areas to which electricity had been cut off for non-payment of bills.

On the Iran border, only 70 people had turned up at Milak-Zaranj, one of the two main border crossings, because of factional fighting, the UN said.

But a convoy of 146 Afghans crossed the border at Islam Qala, the other border crossing west of Herat in western Afghanistan, UNHCR spokesman Kris Janowski said.

Iranian situation

In Pakistan, many of the refugees live in squalid camps, but very few of the estimated 1.5 million Afghans currently believed to be living in Iran are in camps.

Most are scattered around towns and cities all over the country, with the biggest community in the capital Tehran, and many having lived in the country for more than 20 years.

Those who arrived most recently and those with little stake in Iran itself will be the first to think of going back, says the BBC's Tehran correspondent Jim Muir.

Some 40,000 have already spontaneously crossed the border since February, - although some of that movement may have been seasonal labour migration or people simply checking on the situation inside Afghanistan.

But some Afghans in Iran have voiced concerns about security conditions in their own country, and will want to wait and see before committing themselves to return, our correspondent says.

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