By Andrew Osborn and Alexander Marrow

(Reuters) -Russian leader Vladimir Putin told Iran's president over the phone on Friday that Moscow condemned Israeli actions against Tehran, and in a separate telephone conversation told Israel's prime minister that only diplomacy could resolve issues around Iran's nuclear programme.

A Kremlin statement said Putin had spoken to both leaders. Earlier, Kremlin spokesman Dmitry Peskov condemned a "sharp escalation" in tension between Israel and Iran.

Explosions resounded over Tel Aviv and Jerusalem and sirens sounded across Israel following what a military spokesman said was the firing of missiles from Iran. Iran's state news agency IRNA said hundreds of ballistic missiles had been launched in retaliation for Israel's biggest ever attacks on Iran.

A Kremlin statement said Putin told Iran President Masoud Pezeshkian that Russia "condemns the actions of Israel taken in violation of the U.N. Charter" and expressed condolences for those killed.

The statement said Putin, in his conversation with Israel's Prime Minister Benjamin Netanyahu, "stressed the importance of a return to the process of talks and resolution of all issues concerning Iran's nuclear programme strictly through political and diplomatic means".

Russia, the statement said, would remain in close contact with both Iran and Israel.

Earlier Russian statements said the Israeli strikes on Iran were unprovoked and accused Israel of wrecking diplomatic efforts to reach a deal to allay Western concerns about Tehran's nuclear programme.

Initial reports suggested the Bushehr nuclear power plant, which Russia built, had not been hit.

"Russia is concerned and condemns the sharp escalation in tensions between Israel and Iran," Kremlin spokesman Dmitry Peskov told state media.

MOSCOW OFFERS TO HELP CLINCH DEAL

Moscow has repeatedly offered to help the U.S. and Iran reach a deal on Tehran's nuclear programme. It said on Wednesday it was ready to remove highly enriched uranium from Iran and convert it into civilian reactor fuel as a potential way to help narrow U.S.-Iranian differences.

Russia and Iran have grown closer in recent years and Putin and Pezeshkian deepened military ties between their countries in January when they signed a 20-year strategic partnership pact.

But Moscow, which has supplied Iran with weapons and bought Iranian arms, is wary of being sucked into a conflict in the Middle East and the pact contained no mutual defence clause.

In a detailed statement drawn up at Putin's behest, the Foreign Ministry condemned Israel and accused the West of whipping up anti-Iranian "hysteria".

"We strongly condemn the use of force by the state of Israel in violation of the Charter of the United Nations and international law," the ministry said.

"Unprovoked military strikes against a sovereign U.N. member state, its citizens, peaceful cities, and nuclear energy infrastructure are categorically unacceptable.

"The international community cannot afford to be indifferent to such atrocities, which destroy peace and damage regional and international security," it said.

The statement called on both sides "to exercise restraint in order to prevent a further escalation of tensions and the descent of the region into full-scale war".

"In this regard we recall the readiness of the United States to hold another round of talks (on Sunday) with Iran on the Iranian nuclear programme in Oman."

(Reporting by Reuters; Writing by Andrew Osborn/Lucy PapachristouEditing by Mark Trevelyan, Gareth Jones and Ron Popeski)