According to defence lawyer Muhammad Ahmad walad Haj Sidi on Monday, all five men were picked up at their houses and taken to the police headquarters without explanation. Officials refused to comment on the arrests.
But one of the men arrested, Muhammad Jamil walad Mansur, said by cell phone from detention that the arrests were linked to a scheduled visit early next month by the Israeli foreign minister.
"Since we are the main political force opposed to this cursed visit, the regime wanted to present us as a gift," Mansur said before his phone was cut off.
Mauritania, an Arab-dominated West African nation straddling black and Arab Africa, opened full diplomatic relations with Israel in the 1990s.
Despite widespread objections at home, President Muawiya Sidi Ahmad Taya's 20-year old government maintains that the ties allow it to work for change in Israeli-Arab relations.
Three of the five men arrested - Mansur, Muhammad Diduw and Mukhtar walad Muhammad Musa - were arrested in November for allegedly distributing fake photos of prisoner torture, Sidi said.
The three were released in February hours after Mansur and Musa started a hunger strike to protest against what they called their illegal detention.
In November, Aljazeera aired photos of bound, bedraggled prisoners allegedly detained in Mauritania, which authorities said were faked and had been distributed by the trio.
Opposition leaders said they had identified three of the four people in the photographs - wearing handcuffs, hoods and some bound feet to hands - as suspects jailed in alleged coup plots in Mauritania.
The government has jailed scores linked to a violent coup attempt in 2003 and what it says were subsequent attempts this year. Lawyers for some of those jailed also have alleged torture.
The two others arrested on Monday, Abd Allah walad Aminu and Muhammad Abd al-Rahman Niwawi, are both members of a Salafist Islamist group.