Afghanistan has until June 30 to ratify the agreement, the final step before becoming a full member of the organisation that underpins the global system of international trade.
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"Trade-led growth will create new economic opportunities and jobs, especially for women; it will reduce poverty, and increase prosperity," said Afghanistan's Deputy Chief Executive Mohammad Khan Rahmani, in a speech at a WTO meeting in Nairobi where the agreement was passed.
"It will certainly contribute in a major way to dramatically reduce extremism and achieve regional peace and security," he said.
Coming after the launch of the TAPI gas pipeline linking Turkmenistan, Afghanistan, Pakistan and India, the WTO deal is the second big economic agreement for the government this week but the obstacles to growth remain daunting.
Decades of war have destroyed much of Afghanistan's basic infrastructure and fostered a climate of insecurity and corruption that has put investors to flight and forced millions of Afghans to become refugees.
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Once a major horticultural exporter that accounted for 10 percent of the world's dried fruit market in the 1970s, Afghanistan's import-dependent economy, kept afloat by billions of dollars in foreign aid, is among the world's least developed.
The World Bank's 2015 Doing Business report, which measures how easy it is for companies to operate, puts it at 183 out of 189 countries and growth last year was just 1.3 percent, far too slow to provide enough jobs for its fast-growing population.
Aid donors are putting much effort into re-establishing the agricultural sector and developing products like almonds, raisins and pistachios as well as traditional export pillars such as woollen carpets.
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The government has also pledged an ambitious series of reforms to revive the economy, fight corruption and attract investment.
But the World Bank warned in a report from October that the government's reform efforts would take time to have an impact and it was still unclear whether they would mitigate the worsening security climate.
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