The diplomats waited for 30 minutes outside the supreme court in Kabul to see Chief Justice Noor Mohammed Saqib, who was inside meeting with other judges.
Without explanation, Saqib said it was not the right time to meet with the diplomats, who left frustrated. Saqib said the court would contact them if there was any need for a meeting.
The trial of the two Americans, four Germans and two Australians began Tuesday behind closed doors. It was not clear how long the proceedings would last.
"It is moving fast, but talk of what the punishment will be is premature," Saqib told The Associated Press. "We are not saying anything about the trial proceedings or about the punishment until it is finished. The great ulema (clerics) and the judges will decide the punishment according to the principles of Shariat and our Islamic laws."
The Western diplomats said part of their job is to advise their nationals on the legalities of their trials. But for much of the past week, the diplomats have been unable to meet any Taliban official.
"Please pass on the message to the chief justice that we need to know the procedure, so we can pass it on or have it passed on to the detainees," said Alastar Adams, an Australian diplomat.
"An explanation of the judicial process, what is happening in this case, we have no official word at all. We have some idea from press reports that the case has commenced, we have had no official advice up to this point," he said. "We are not here to interfere with the legal process," he said.
In Washington, a U.S. State Department official called for a fair trial.
"We call upn the Taliban to ensure the proceedings follow the rule of law and are fair and transparent," said the official, who declined to be identified.
The parents of the two American women, Dayna Curry, 29, and Heather Mercer, 24, visited their daughters last weekend, and Adams saw the two imprisoned Australians last week.
Curry's mother, Nancy Ellen Cassell, a teacher from Thompson's Station, Tenn., and Mercer's father, John Mercer, of Vienna, Va., are the only family members who have come to Afghanistan so far.
After trying for six days to arrange a meeting with a Taliban foreign ministry official familiar with the legal procedures, the diplomats decided to approach the chief justice on their own, said Helmut Landes, a German diplomat.
Adams and Landes were accompanied by U.S. diplomat David Donahue. All are stationed at embassies in neighboring Pakistan.
The eight foreign aid workers of Shelter Now International, a German-based Christian organization, were arrested last month along with 16 Afghan employees of the same organization.
The only other trial of foreigners under Taliban rule occurred in March 1997, when two French nationals of the Paris-based Action Against Hunger were tried on charges of immoral conduct.
The two men were jailed for 26 days before their trial began. It lasted less than an hour, and the judge sentenced them to time served and ordered them expelled immediately.
On Tuesday, Saqib said the aid workers were entitled to a Taliban lawyer if they wanted one.
"They have the complete right to defend themselves in court. If they want to use a lawyer we have no objection," Pakistan Afghan Islam Press quoted him as saying. "They can even bring in foreign, non-Muslim lawyers to defend themselves."
AIP quoted Saqib as saying the punishment would accord with the crime. The Taliban say supreme leader Mullah Mohammad Omar has the final say no matter what the court decides.
There was no indication the accused had yet been called to appear and it was not clear if or when diplomats, family members or reporters would be allowed in to observe the trial.
Saqib told AIP it was not necessary for anybody besides the accused to attend court.
"However, in case the judges and the religious scholars feel it necessary for anybody else to attend court proceedings they will be allowed," he said.
The Taliban's investigation into the Shelter Now International case worried other relief organizations, and led to the expulsion of more than 20 aid workers with two other groups.
Recognized as a legitimate government by just three countries, the Taliban rule about 95 percent of Afghanistan and want to establish a purist Islamic state.
Their strict interpretation of Islam has often earned them international condemnation, especially for human rights abuses and the destruction of the country's pre-Islamic heritage.
The U.N. refugee organization, one of the few groups still operating in the impoverished county, distributed 4,500 tents on Wednesday to refugee Afghans driven from their homes because of drought, hunger and war.
The tents will shelter about 27,000 people, said Yusuf Hassan, spokesman for the United Nations High Commissioner for Refugees.
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