Two American women are behind bars in Afghanistan. Their alleged crime? Christian preaching. 

The imprisonment of the two Americans, six other foreign aid workers and 16 locals who worked for their organization by the Islamic fundamentalist Taliban government — and the expanding investigation into possible proselytizing by all foreign aid organizations — has alarmed U.S. officials. 

"We are a little surprised at the breadth," said John Kincannon, a spokesman for the U.S. Embassy in Pakistan. 

Mohammed Wali, the Taliban's minister for the promotion of virtue and prevention of vice, issued a warning to all organizations suspected of teaching Christianity that their aid projects will be scrutinized by three Taliban ministries — security, vice and virtue, and intelligence. 

Among those notified was the United Nations. 

The Taliban arrested 24 workers of Shelter Now International one week ago — the American women, four Germans and two Australians, plus the 16 locals — and charged the foreign nationals with trying to convert Muslims to Christianity. The punishment, if found guilty, is death. However, Taliban officials said that the foreigners would be deported if convicted. 

Afghan visas for diplomats from Australia, Germany and the United States were approved on Monday. Foreign Minister Wakil Ahmed Muttawakil told reporters that diplomats will be allowed to meet Taliban officials in Kabul, but cannot visit the accused missionaries in prison. 

"This is what we have been told, but we will go anyway," said Howard Brown, the Australian High Commissioner in Pakistan. 

It hasn't been decided when the diplomats will travel to Kabul, or who will represent which country. 

"We will continue to press vigorously for consular access to the two Americans," Kincannon said. 

Still unclear are what specific charges are to be laid against the 16 Afghan staff of Shelter Now, which is run by the German-based Christian charity Vision for Asia. So far no one has been allowed access to the detained aid workers. 

Muttawakil also said organizations like the U.N. World Food Program will be questioned about their knowledge of Shelter Now activities. 

Muttawakil said the WFP gave food for distribution to the aid organization knowing full well that the group was a Christian missionary organization. That, he said, makes the WFP a party to Shelter Now's preaching. 

The WFP flatly denied any involvement in religious education. 

"The WFP has no religious intentions whatsoever," Francis Mwanza, a spokesman at its Rome headquarters, said Sunday. 

The evidence, seized from the office of Shelter Now, included compact discs, cassettes and literature — all containing stories about Christianity and the coming of Jesus Christ, and all translated into local languages. 

The Associated Press contributed to this report.