In this story:

• Islamic group claims responsibility for attack
• United States trying to improve relations

TEHRAN, Iran (CNN) - A senior Iranian official has condemned a recent attack on a bus carrying Americans and others, saying that Iran will take all necessary steps to protect visitors to the country.

Deputy Interior Minister Mostafa Tajzadeh was quoted by the daily Iran News on Tuesday as saying anyone granted a visa to Iran had the right to personal security and safety.

"The government is obliged to provide security for all countries' citizens. The lives of the people must be protected even if they are our opponents," Tajzadeh told the English- language newspaper.

A group naming itself after Islamic extremists known for political assassinations said it was behind the attack, newspapers reported on Tuesday.

"A group called Fadaeeyan-e Eslam (Devotees of Islam)...in a letter claimed responsibility for the attack on the convoy of... Americans who had travelled to Tehran," Hamshahri newspaper said. Other newspapers carried similar reports.

Islamic militants chanting "Death to America" used clubs and metal bars on Saturday to smash the windows of the bus carrying a group of 13 non-Iranians, including U.S. citizens, after hardline newspapers accused them of being spies.

A number of Iranian officials condemned the attack. The Qods daily reported on Tuesday that conservative members of parliament's foreign affairs commission were planning to summon Foreign Minister Kamal Kharrazi to account for the visit.

In the meantime, U.S. Secretary of State Madeleine Albright, in a new move aimed at improving ties with Tehran, has recommended that President Bill Clinton remove Iran from the U.S. list of major illicit drug-producing countries, a senior U.S. official said on Monday.

The official told Reuters a new U.S. survey has concluded that Iran has eradicated much of the country's illicit poppy cultivation and thus it "no longer meets the statutory justification" for inclusion on the U.S. list.

The official said it was hoped Iran would see the decision as evidence that the United States makes judgments on the basis of facts and "they are not based on some preordained desire to isolate Iran."

This was the latest gesture by Washington in a hesitant, slow-moving diplomatic effort to improve relations between the two countries since moderate Mohammad Khatami, became Iran's president in 1997.

Washington broke off diplomatic relations in April 1980, five months after militant students stormed the U.S. embassy in Tehran. Switzerland currently looks after U.S. interests in Iran.

Reuters contributed to this report.