Bahraini authorities on Sunday re-arrested a prominent Sunni opposition leader for "violating the law", just three weeks after his release from jail, the interior ministry said on Twitter.
Ibrahim Sharif, who used to head the Waed secular group, had been freed on June 19 after spending four years in jail over his involvement in 2011 Shiite-led anti-government protests.
He had played a prominent role in the month-long protests and was later among a group of 20 activists tried for plotting to overthrow the Sunni rulers of Shiite-majority Bahrain.
The interior ministry did not say why he was re-arrested.
Opposition sources said he was taken back to prison after he criticised the government during a ceremony for one of the victims of unrest that rocked the kingdom, home to the US Fifth Fleet.
Waed party said Sharif was remanded him in custody for 48 hours pending investigations on charges of "inciting hatred against the regime".
"The arrest of Sharif is an attempt to silence him and confiscate the freedom of speech guaranteed by the constitution," said Waed in a statement.
Bahrain's opposition is demanding a constitutional monarchy and an elected prime minister.
At least 89 people have been killed in clashes with security forces since 2011, while hundreds have been arrested and put on trial, rights groups say.