The possible return of Hassan Meshaima after months of voluntary exile in London could mark a new phase for the protest movement as the Gulf island's monarchy tries to open talks to end the most severe political crisis in decades in the strategic nation - which is home to the U.S. Navy's 5th Fleet.
In a sign of Washington's deep ties to Bahrain, U.S. Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, was in the kingdom for meetings with ruling officials.
Meshaima, the head of a Shiite group known as Haq, is considered more hard-line than the main Shiite political bloc that has taken a lead among the protesters. The opposition currently appears divided on whether to demand an end to the Sunni monarchy or offer it a chance to remain in exchange for handing powers to the elected parliament.
Shiites account for about 70 percent of Bahraini's 525,000 people, but have long complained of systematic discrimination and other abuses by the Sunni dynasty that has ruled for more than two centuries.
Meshaima is among a group of Shiite activists who were accused of plotting to overthrow the ruling system. Authorities, however, have suspended a trial on the charges.
The government spokeswoman, Maysoon Sabkar, said that authorities have no plans to take Meshaima into custody if he returns.
Security and judicial officials in Lebanon, however, said they have confiscated Meshaima's passport on an Interpol warrant.
Meshaima arrived in Beirut on Tuesday en route to Bahrain, where protests erupted last week inspired by the uprisings in Tunisia and Egypt.
The Lebanese officials spoke on condition of anonymity because of the sensitivity of the subject. It was unclear whether Bahrain will take steps to lift the international arrest warrant.
Khalil Marzook, a senior member of Bahrain's biggest Shiite opposition bloc, Al Wefaq, called on Bahrain's government to lift the warrant.
Sabkar, the government spokeswoman, said that Friday has been declared an official day of mourning for seven demonstrators killed in clashes with security forces.
The government later said it would begin next week a previously announced plan to give 1,000 dinars (nearly $2,660) to each Bahraini family.
On Wednesday, Bahrain released at least 100 prisoners, including 23 Shiite activists on trial since last year for plotting against the state. Meshaima and other opposition figure were being tried in absentia.