DUBAI (Reuters) -Iran will respond promptly to any threat against its security, the foreign ministry said on Monday, after the United States, Israel and Britain blamed Tehran for an attack on an Israeli-managed tanker off the coast of Oman.

Tehran has denied any involvement in the suspected drone attack on Thursday in which two crew members - a Briton and a Romanian - were killed.

The United States and Britain said on Sunday they would work with their allies to respond to the attack on the Mercer Street, a Liberian-flagged, Japanese-owned petroleum product tanker managed by Israeli-owned Zodiac Maritime.

British Prime Minister Boris Johnson described the incident as "clearly an unacceptable and outrageous attack on commercial shipping".

"Iran should face up to the consequences of what they've done," Johnson told reporters on Monday.

Britain summoned the Iranian ambassador on Monday. Later, Iran summoned the British Charge d'Affaires and Romania's top envoy in Tehran over their countries' "accusations against the Islamic Republic", Iran's semi-official Fars news agency reported.

"Iran has no hesitation in protecting its security and national interests and will respond promptly and strongly to any possible adventure," Iranian state television quoted foreign ministry spokesman Saeed Khatibzadeh as saying.

Israeli Prime Minister Naftali Bennett had accused Tehran of "trying to shirk responsibility" for the attack, and called its denial "cowardly". Israel's foreign minister said on Sunday the incident deserved a harsh response.

ISRAEL WILL 'SETTLE THE SCORE'

Israel Defence Minister Benny Gantz said the attack was an intensification of what he called Iran's escalation and accused Tehran of intending to hurt and kill civilians.

"Israel has a variety of tools and options to defend its citizens, and we will settle the score with anyone who tries to harm us at the time and place and in the way that suits us and our security," Gantz told the Israeli parliament.

An unidentified Iranian official told Iran's Nournews news agency earlier that Tehran considered "the threats of Western officials and the Zionist regime (Israel) to be more of a propaganda gesture".

"And Washington and London will be directly responsible for the consequences," the official told Nournews, which is close to Iran's Supreme National Security Council.

In Washington, Secretary of State Antony Blinken predicted a "collective response" and said he did not think the incident necessarily signaled anything about Iran's incoming President Ebrahim Raisi, who takes office on Thursday.

Iran and Israel have exchanged accusations of carrying out attacks on each other's vessels in recent months.

Tensions have increased between Iran and Israel since 2018, when then U.S. President Donald Trump ditched Tehran's 2015 nuclear deal with six world powers and reimposed sanctions that have crippled Iran's economy.

Israel has voiced concerns about efforts by Iran and U.S. President Joe Biden's administration to revive the nuclear pact, under which Iran curbed its sensitive nuclear work in exchange for the lifting of sanctions.

"In any agreement, should there be one, with Iran, it must also be based on the removal of its threat on the region," said Gantz.

(Additional reporting by Guy Faulconbridge in London and Ari Rabinovitch in Jerusalem; Writing by Parisa HafeziEditing by Peter Graff, William Maclean and Sandra Maler)