Moratinos said: "We got a very positive response from the Syrian authorities that they want to cooperate and be constructive in the consolidation of implementation of UN Security Council Resolution 1701."
Resolution 1701 refers to the truce that came into force on August 14.
After talks with Bashar al-Assad, Syria's president and Walid Muallem, Syria's foreign minister, in Damascus on Saturday and Sunday, Moratinos said: "They will cooperate in all fields in order to make the situation in Lebanon a real success."
The Spanish minister, who also came to the capital in March, is the most senior Western official who continues to visit the Syrian capital and drew strong US criticism earlier this year for his defiance of Washington's efforts to sideline the Syrian regime.
Moratinos again insisted that Damascus could not be left out of any lasting Middle East peace settlement.
He said: "There will not be a final solution in the Middle East if there is not a solution of the Syrian-Israel relationship, so we need a comprehensive peace.
"They [Assad and Muallem] conveyed to me the genuine wish and will to work in a constructive and positive manner."
Damascus provides a base in exile for a number of Palestinian leaders and has seen considerable diplomatic activity in recent days aimed at securing agreement on a national unity government in the territories acceptable to donor countries to the area.
Clashes in Palestine earlier this month between Hamas and Fatah had prompted fears of a breakdown in talks.
Moratinos insisted that while many governments in the West were keen to see a broad coalition replace the existing Hamas-dominated government, the negotiations were a matter for the Palestinians.
He said: "I think we are waiting for the Palestinians themselves to get to some conclusion of a national unity government. But it's up to the Palestinians, the only thing we can do is to encourage them."
Syria 'stirring trouble'
Ahmad Fatfat, Lebanon's acting interior minister, has said Syria is bent on destabilising Lebanon, whose security forces, he said, are not yet strong enough to prevent more possible assassination attempts.
Fatfat said that he had recently received a message from someone close to the Syrians, telling him and Fouad Siniora, Lebanon's prime minister, to "take care".
The message had said the Syrians were "more angry than before February 14, 2005", the date of Rafiq al-Hariri's, Lebanon's former prime minister, assassination.
He did not say what had angered Damascus, but tensions have risen in recent weeks amid Syrian criticism of Siniora's government as unrepresentative and as serving Israel's interest.
Fatfat, a Sunni member of the anti-Syrian Future Movement led by al-Hariri's son Saad, said he was sure Syria still had informants in Lebanon, despite its troop pullout last year.
He said: "The Lebanese security services are more powerful now, but not enough to control everything."
Fatfat said last month's attempted assassination of a senior interior ministry intelligence officer was likely to have been "a political message related to the [al-Hariri] investigation."
Syria denies any involvement in al-Hariri's killing or in a subsequent series of assassinations and attacks on Lebanese politicians and journalists hostile to Syria's role in Lebanon.