Iran has made arrests over a scientist's assassination last week blamed on Israel and the US, parliament speaker Ali Larijani said Monday, vowing his country would avenge the death using "non-terrorist" tactics.
He did not specify how many people were arrested or when the arrests were made, or give any details on the suspects' identities or nationalities.
"We have discovered some clues and some arrests have been made. Investigations are ongoing," Larijani told Iran's Arabic-language broadcaster Al-Alam.
Various Iranian officials have blamed Israel and the United States for the 11 January killing of Mostafa Ahmadi Roshan, a 32-year-old deputy director of Iran's main uranium enrichment plant.
Ahmadi Roshan died along with his driver after assassins on a motorbike fixed a magnetic bomb to his car.
It was the fifth such attack targeting Iran's scientists in the past two years. Four other scientists -- three of them involved in Iran's nuclear programme -- died in the attacks, while one managed to escape.
Iranian military commanders have said they are looking at "punishing" those responsible.
But Larijani said Iran would not resort to terrorism to take its revenge.
"We will not hesitate in punishing the Zionist regime [Israel] so that it realises such actions have clear responses. There will definitely be a response but our action will be of a non-terrorist nature," he said.
On Saturday, the deputy chief of Iran's joint armed forces, Masoud Jazayeri, said Iran was mulling a response to hold the US, Israel and Britain "accountable" for their perceived involvement in the attacks.
Iran's supreme leader, Ayatollah Ali Khamenei, on Thursday blamed the US and Israeli intelligence services for the latest killing.
He said Iran would "continue with determination" its nuclear activities, which Western governments suspect mask a drive for a weapons capability despite Tehran's repeated denials.
Washington has issued strongly worded denials of any role in the murders. Israel, widely seen as the prime suspect, has neither denied nor confirmed involvement, in line with its policy of not commenting on intelligence matters.