WASHINGTON- Pakistan has begun reducing the flow of Afghan immigrants, fearing that the pullout of U.S. troops from Afghanistan might trigger an overload of new arrivals.Officials are concerned the withdrawal of U.S. troops and decline in foreign aid will prompt an influx of Afghans into Pakistan, which already has the world's largest refugee population. Over seven million people have entered Iran and Pakistan from Afghanistan since the Soviet invasion in 1979. "I believe this influx is already here. We are in a tight situation ourselves, so having this influx is not desirable to anyone in the world," said Mohammed Abbas Khan of Pakistan's Office of the Chief Commissioner for Afghan Refugees.Calls to Pakistani officials from local authorities on illegal Afghan settlements have increased dramatically in recent weeks, and officials in Northwestern Pakistan have established policies making it harder for refugees to rent apartments. New screening measures at the border between the two counties have been established, and police in the Pakistani city of Karachi actively search for illegal migrants, according to a UPI report today. The actions come as Iran is pressing its 800,000 Afghan refugees to relocate. There are 1.6 million legally registered Afghan refugees in Pakistan, but officials believe one to three million more are present illegally. "We want them to go back to their own country," said Sartaj Aziz, foreign affairs advisor to Prime Minister Nawaz Sharif, noting the burden to Pakistan's economy and opportunity presented to Islamist militants, with ties to Afghanistan, to operate in Pakistan.