The statement was referring to several recent arrests of individuals suspected of spying for the Jewish state.
Al-Hariri, a Sunni Muslim construction magnate who had been Lebanon’s prime minister on two occasions, was killed with 22 other people in a bomb attack in Beirut in February 2005.
'Mobile phone link'
The Der Spiegel report quoted an un-named source close to the UN tribunal as saying that Lebanese investigators found a link between eight mobile phones used at the time of the bombing and a network of 20 other phones belonging to Hezbollah agents.
The report named the suspected mastermind of the attack as Hajj Salim, believed to be the commander of the Islamic Resistance, Hezbollah's military wing.
Prior to the formation of the special tribunal, interim reports from investigators leading the UN Independent Investigation Commission suggested that Lebanese and Syrian security officials may have planned the killing of al-Hariri.
At the time of al-Hariri's death, Damascus had thousands of troops and intelligence officers deployed in Lebanon.
Widespread public anger in Lebanon after the assassination led Syria to pull its forces out of Lebanon in April 2005, ending a 29-year presence in the country.
The Der Spiegel report comes before a June 7 parliamentary election in Lebanon, in which a Western-backed parliamentary majority faces a bloc led by Hezbollah, which is supported by Iran and Syria.
Calls for arrest
The special tribunal on April 29 ordered that four Lebanese generals suspected of involvement in the bombing be released from the custody of the Lebanese authorities.
Responding to the magazine report, Israel's foreign minister said that an international arrest warrant should be issued for Hassan Nasrallah, Hezbollah's secretary-general.
"The report in Der Spiegel on Nasrallah's direct involvement in the assassination of Hariri should raise concern in the entire international community," Avigdor Lieberman said.
"He should have an international arrest warrant issued against him, and if not, he should be arrested by force," he said.