DUBAI (Reuters) - Bahrain's foreign ministry summoned Iraq's ambassador in Manama to protest against remarks by Iraqi officials denouncing the execution of men convicted of a 2014 bomb attack, state news agency BNA said on Monday.

The execution on Sunday of three men, whose attack killed three policemen, has drawn condemnation from rights groups. Iran called it a "reckless" act.

British Foreign Secretary Boris Johnson said Britain opposes the death penalty and he "raised the issue with the Bahraini Government."

Iraqi Vice President Nouri al-Maliki called the execution "an ugly crime" and said it put the Bahraini government in a position of being accused by the international community of systematic killing of its opponents.

The Bahrain foreign ministry said Maliki's remarks and comments by the Iraqi foreign ministry spokesman amounted to an "unacceptable interference" in Manama's internal affairs.

Bahrain says the execution was carried out after a lengthy judicial process that had convicted the three men - Abbas al-Samea, 27, Sami Mushaima, 42, and Ali al-Singace, 21. The attack killed an Emirati police officer and two Bahraini policemen.

"The undersecretary of Regional and GCC Affairs, Ambassador Waheed Mubarak Sayyar, asserted the Kingdom of Bahrain's condemnation and its deep rejection of the remarks ... and demanded they be conveyed to the Iraqi government," BNA said.

Bahrain, facing demands by its Shi'ite Muslim majority for political and economic reforms, has recently accused Iraqi groups of providing military training and support for militants behind bomb attacks that have killed several policemen in recent years.

Relations between Baghdad and Iraq's Sunni Muslim Arab neighbors, including Bahrain, have been frosty since U.S. forces toppled Sunni President Saddam Hussein in 2003 and replaced him with a Shi'ite-led government.

(Reporting by Sami Aboudi; Editing by Tom Heneghan)