"In my opinion this visit to Syria is a Russia-organized event, the goal of which is to voice support for Russia's stance over Syria," said the head of Latvia's interior police force, referring to the March 12 visit by Mamikins.
"It's despicable that a MEP from Latvia is taking part in such activities," said Mežviets.
He said that the Latvian public should reconsider whether people like this should be allowed to serve as MEPs.
Mežviets also used the interview to point out that Latvians are too eager to criticize their own country, which according to him ultimately makes us more vulnerable.
"There has to be criticism, however it must be constructive," Mežviets said.
He also claimed that Russia might use Latvia's centenary events for its propaganda purposes.
Meanwhile Mamikins blasted Mežviets as "incompetent" and said he and his colleagues will go to court.
"I have not seen a more incompetent [..] employee. Even now we [..] together with the colleagues who went, are planning to go to court in Latvia against the head of the Security Police, because those are shameless lies," Mamikins told rus.lsm.lv.
"We had no meeting with Russia, and the Russian Federation doesn't have anything to do with this meeting," he said.
As reported, Mamikins visited Syria's authoritarian ruler Bashar al-Assad last year-end, and once again on March 12 this year. In the first visit he was also accompanied by Estonian MEP Yana Toom of the ruling Center Party.
Another opposition MEP, Tatjana Zdanoka, visited Assad last July.
(The story was updated on March 14 at 11.39 a.m. with Mamikins' comment.)