A series of explosions in the Bahraini capital Manama on Monday killed two Asian expatriates and wounded a third, police said, describing the blasts as "acts of terror".
"There were five explosions from home-made bombs... on Monday morning" in the Gudaibiya and Adliya districts of Manama, said a police statement.
The blasts' three victims were all Asian expats, it added.
An initial investigation showed an "improvised explosive device (IED) exploded" when a man kicked it, police said. He died at the scene.
A second victim sustained serious injuries from another blast in a separate area of the city and was pronounced dead at the hospital, the statement said.
"A third explosion in Adliya seriously injured a man who works as a cleaner," it said.
Police gave no details of the intended targets of the blasts or who might be responsible.
Bahrain's main Shiite opposition group Al-Wefaq condemned the attacks but cautioned that "due to the absence of independent human rights and media parties, it is difficult to clearly determine the truth behind the incidents."
In a statement, Al-Wefaq said it "rejects violence" and "condemns these incidents."
Signup to our newsletter and follow us on Facebook and Twitter!
Amnesty International called for a thorough and impartial probe into the attacks, which it said "show a total disregard for human rights and the basic principles of humanity."
"The authorities must ensure that an independent, impartial and thorough investigation is conducted," said Amnesty's Middle East and North Africa deputy director Hassiba Hadj Sahraoui.
The London-based watchdog also demanded that "those responsible are brought to justice in proceedings that comply with internationally recognised standards for fair trial and with no possibility of the death penalty."
Bahraini police have been targeted in past months in what officials have described as "terrorist acts."
In October, two policemen died after sustaining serious injuries from an IED attack.
In April, an IED exploded in a Shiite village on the outskirts of Manama seriously wounding two other policemen.
Sporadic protests have intensified since a March 2011 crackdown ended a month of protests in central Manama demanding democratic reforms.
According to the International Federation for Human Rights, 80 people have died in Bahrain since the start of the violence on February 14 last year.
Bahrain's interior ministry says more than 700 people, including a number of police officers, have been wounded in the protests since the beginning of 2012.