France has warned Syria it will not tolerate its agents harassing those who are protesting against the rule of President Bashar al-Assad.
The warning followed media reports that a group of activists had been filmed, insulted and attacked in Paris.
Earlier, an Amnesty International report accused Syria of a campaign of intimidation against activists abroad.
It quoted the activists as saying that Syrian embassy staff had threatened them and their relatives in Syria.
Meanwhile, Russia has said it will not support a draft resolution condemning Syria's suppression of pro-democracy protests, which is to be put to the UN Security Council on Tuesday.
French foreign ministry spokesman Bernard Valero, quoted by Agence France-Presse, said Syrian activists had been given more police protection in the wake of the alleged intimidation, which is now being investigated.
He said: "We would not tolerate a foreign state organising acts of violence or intimidation on our territory, and we have made this known in the clearest possible terms to Syria's ambassador in Paris.
"The right to protest freely and peacefully in safety is fully guaranteed by the French constitution, and it is also obvious that France supports the Syrian people's hopes for freedom."
Le Monde newspaper had reported an attack on a small group of Syrian protesters in a square in central Paris.
In its report entitled Syria: The long reach of the Mukhabaraat, Amnesty International details the cases of 30 Syrian activists in eight countries, in Europe and North and South America, who have been systematically monitored and harassed by Syrian embassy officials and others believed to be acting on behalf of the Syrian regime.
The report says the dissidents' relatives in Syria have also, in some cases, apparently been exposed to harassment, detention and even torture. Some activists say they were directly threatened by embassy officials.
Naima Darwish, who set up a Facebook page to call for protests outside the Syrian embassy in Santiago, Chile, told Amnesty she was contacted directly by a senior official who asked to meet her in person.
"He told me that I should not to do such things. He said I would lose the right to return to Syria if I continued."
Amnesty has called on host countries to take stronger action against the Syrian embassies accused of orchestrating the intimidation campaign.
Robert Ford, the US ambassador in Syria, also renewed criticism of the Syrian government, calling on it to stop its "incredible repression" and allow a political process of transition to move forward peacefully.
Import ban rescinded
Meanwhile, Russia said it would not support Tuesday's UN draft resolution.
Deputy Foreign Minister Gennady Gatilov said that Moscow "cannot support a text" that did not urge other countries not to become involved in Syria's internal affairs.
But it is unclear whether Moscow will veto the resolution.
On Tuesday, Turkish media reported that a colonel who had defected from the Syrian army was calling for a united front against Mr Assad.
"Opponent forces in Syria should get united and close ranks until the regime collapses," Col Riad al-Asaad, who is sheltering in Turkey, told the Anatolia news agency.
Separately, Syria has withdrawn a ban it imposed on many consumer goods and raw materials, amid reported discontent over rising prices.
The ban was intended to preserve foreign currency reserves.
Syria is under international pressure to stop using force to suppress protests that began six months ago.
The UN estimates that more than 2,700 people have been killed across Syria since the crackdown began.
On Tuesday the Syrian Observatory for Human Rights said three soldiers and one civilian had been killed in fighting between government troops and army defectors in the Jabal al-Zawiya region in north-west Syria.
The government says it is in the process of introducing reforms and is speaking to members of the opposition - it blames the unrest on armed gangs.