Walid al-Muallem, Syria's foreign minister, said: "As a state, we will irrefutably prove the party involved in this crime and who stands behind it.
"We hope that you will soon hear the results of this mighty effort."
Al-Muallem made the remarks after meeting Manouchehr Mottaki, his Iranian counterpart, who travelled to Damascus from Beirut where he attended Moghaniyah's funeral.
Al-Muallem, however, declined to say whether the authorities have apprehended anyone in connection with the attack or whether there had been a breach in the security apparatus of tightly controlled Syria.
"I cannot comment to preserve the secrecy of the investigation. The fighter Imad Moghaniyah was the target of lots of intelligence agencies. He was a backbone of the Islamic resistance," he said.
In a tribute to Moghaniyah via video link, Hassan Nasrallah, the secretary-general of Hezbollah, said on Thursday that Israel killed Moghaniyah and that Hezbollah was ready for "open war" with Israel.
"Zionists, if you want this type of open war then let the whole world hear: let it be an open war," he said.
'Right of self-defence'
Nasrallah said the assassination was carried out outside the natural battle ground between the two sides.
"We have the right, like all human beings, of self-defence and, God willing, we will do whatever is required to defend our brothers, leaders, people and our country," he said.
Nasrallah said that while Moghaniyah's assassination was a painful blow, it would not weaken Hezbollah or its military structure.
Western intelligence officials say Moghaniyah masterminded suicide bombings in Lebanon during the 1974-1990 civil war that killed hundreds of Americans and French, as well as hostage takings of Westerners and 1985 hijacking of a TWA airliner in which a US navy diver was killed.
Western and Israeli intelligence also accused him of planning suicide bombings against the Israeli embassy and a Jewish cultural centre in Argentina that killed over 100 people.
Over the past 15 years, he is believed to have moved in secret between Lebanon, Iran and Syria.
Speaking to Al Jazeera on Friday, Imad Fawzi Shueibi, president of the Centre of Strategic Studies in Damascus, said that Moghaniyah's assassination was a turning point in the rules of the game in the region's conflict.
He said: "The US was the only state that welcomed the assassination ... which is dangerous.
"Whoever committed this crime, Israel or another state, is trying to change cards and to make a huge problem for the whole of the region."
Israel has denied Nasrallah's accusation and announced a state of alert in the ranks of its forces after his threats, calling on its citizens to exercise caution.
Western countries accuse Syria of being the main weapons supply route for Hezbollah, in contravention of a UN resolution.
Syria says no weapons cross its territory bound for the Hezbollah, which is also supported by Iran.
Syria participated in the US-sponsored Annapolis peace conference in November and renewed its offer to Israel for normal relations in return for the Golan Heights, which Israel occupied in 1967.