Lebanese Druze leader Walid Jumblatt has accused Syria of terrorising Arab countries and has urged the head of the Arab League, Amr Moussa, to intervene.
Walid Jumblatt said Syria was behind many recent assassinations
Mr Jumblatt, Lebanon's most prominent anti-Syrian politician, said Syria was "taking the path of terrorism in order to evade international pressure".
He said Mr Moussa "must go to Damascus to stop the murders in Lebanon".
A UN inquiry has implicated Syrian officials in the killing of former Lebanese PM Rafik Hariri in February.
Many Lebanese also blame Syria for the murder of the anti-Syrian journalist and MP, Gibran Tueni, earlier this month.
Damascus has denied any involvement in either killing.
'We will not cave in'
Mr Jumblatt charged that Syria controlled a variety of "instruments and terrorist factions capable of scaring Arab regimes", in an interview with the Lebanese satellite channel LBCI.
He told Lebanon's Daily Star newspaper that "we have received several messages threatening public bombings, and our response to that is that we will not cave in under their terrorist ways".
"We accuse this regime of all the assassinations that took place in Lebanon, yesterday, now and tomorrow," Mr Jumblatt said.
He criticised initiatives by Arab states to shield Syria from international pressure.
"The only thing that should be adopted by the Arab mediators is pushing Syria into really co-operating with the international probe," he said.
Last Friday, the UN Security Council voted to extend the UN inquiry's mandate by six months.
In a unanimous vote, it said Syria had still to provide the UN's commission with "the full and unconditional co-operation" it requires, or face unspecified action.