Ebadi, who had been chosen by the family of Haleh Esfandiara to defend the academic, said her client was being deprived of her civil rights, the ILNA news agency quoted her saying.

"My client is being detained without having access to a lawyer," she said in a statement.

Esfandiari is one of two dual citizens charged with spying in cases that have further increased tension between Iran and the United States, which is leading international efforts to isolate the Islamic Republic over its sensitive nuclear work.

The United States, which broke diplomatic ties with Iran after their embassy was occupied shortly after the 1979 Islamic revolution, has called for their release and denied that they are spies.

Iran, which does not recognize dual nationalities, has told Washington the arrests are none of its concern.

Tehran says Washington is using intellectuals and others to carry out a "soft revolution" to topple the Islamic state. A charge of spying could carry the death sentence.

Another Iranian-American, journalist Parnaz Azima, is being investigated for "anti-revolutionary activities." Iran confirmed on Sunday it held a fourth dual citizen, who an Iranian news agency had said was being probed over security-related issues.

Esfandiari, the director of the U.S. Woodrow Wilson International Centre for Scholars' Middle East program, was detained on May 8 while visiting the Iranian capital.

Ebadi, saying Esfandiari's family had chosen her as defence lawyer, said she had gone to Tehran's Revolutionary Court on Monday but that she had only been able to speak with the interrogator in the case on the phone.

"He told me Mrs Esfandiari does not need a lawyer and they didn't even let me enter the building to see him," Ebadi said in the statement carried by ILNA.

"The responsibility for protecting her life, health and security is on the judiciary officials who, by ignoring the law, have deprived her of her civil rights," the statement said.

Speaking about another security-related case, Iran's justice minister last year said the suspect could not have access to a lawyer during the interrogations.

Some analysts link the arrests of U.S.-Iranians to the detention of five Iranians by U.S. forces in Iraq in January.

Iran says the five are diplomats but U.S. officials say they were involved in supporting militants inside Iraq. Iran has dismissed any linkage between the detentions in Iraq and any other issues.