Lebanon's Hezbollah rejects charges in a German magazine that it was behind the 2005 killing of former Lebanese Prime Minister Rafiq al-Hariri and says the "fabrications" were made to try to influence next month's general election.

A suicide truck bomber killed Hariri and 22 other people in Beirut in February 2005. A UN investigation into the assassination first implicated Syrian and Lebanese officers but it later held back from giving any details on its findings.

The UN Special Court for Lebanon (SCL) began work in March and one of its first actions was ordering the Lebanese authorities to release four pro-Syrian generals who had been held in connection with the case after saying it had no evidence against them.

"The special UN tribunal investigating the murder of former Prime Minister al-Hariri has come up with surprising new conclusions, and is keeping them secret," the magazine wrote in an article at the weekend.

"According to information Der Spiegel has obtained, investigators believe that Hezbollah was behind the murder."

Hezbollah rejected the allegations and said the timing of the report was aimed at influencing Lebanon's June 7 general election and at covering up the arrest in recent months of more than two dozen Lebanese on suspicion of spying for Israel.

Hezbollah and its allies hope to win the election, widely believed to be too close to call, and unseat the country's anti-Syrian coalition that has held a majority in parliament since 2005.

"These are nothing but police-like fabrications made in the same dark room that for four years fabricated similar stories regarding the (involvement of) Syrians and the four officers," Hezbollah said in a statement in Beirut.

"Publishing these accusations and attributing them to sources close to the international court dents the credibility of the tribunal and its work and requires firm and clear action towards the publishers of these evil fabrications," it added.

Lebanese Foreign Minister Fawzi Salloukh said Der Spiegel's claim was "totally false" and that UN investigators did not question any member of Hezbollah in connection with the Hariri assassination.

Salloukh was speaking in the Syrian capital Damascus, where he was attending a foreign ministers' meeting for the Organisation of the Islamic Conference.

The news weekly, quoting sources close to the tribunal and then backed up by examining internal papers, said that Lebanese investigators found a link between eight cell phones used in the area at the time of the attack and a network of 20 other phones believed to belong to Hezbollah's "operative arm".