A London-based reporter for Russia's state-owned English-language channel RT quit Friday in protest at its coverage of the Malaysia Airlines crash in Ukraine.

Sara Firth is the second person since March to publicly resign from RT, formerly known as Russia Today, over its coverage of the Ukraine crisis.

World powers are strongly considering delaying a Sunday deadline to reach a deal on Iran's nuclear program until November, Russian media reported, citing Moscow's negotiator at the Vienna talks.

"The dominant point of view is that we need a new control date in November. That is, a year from reaching the Geneva agreement," RIA Novosti quoted Deputy Foreign Minister Sergei Ryabkov as saying on Friday.

German Chancellor Angela Merkel called Friday for an immediate ceasefire in Ukraine to facilitate a probe into the apparent downing of a passenger plane in the rebel-held east of the country.

Merkel said Russia in particular must do its part to bring about a "political solution" to the conflict in Ukraine, adding that Moscow bore responsibility "for what is happening" in the strife-torn country.

U.S. President Barack Obama hinted Friday that a Malaysian passenger plane flying over eastern Ukraine was shot down by pro-Moscow separatists, as the U.N. Security Council demanded a full, independent and international probe into the deadly incident.

At a press conference, Obama said a missile fired from rebel-held territory in Ukraine downed the Malaysian jet as he pressed for an international investigation.

British Prime Minister David Cameron said Friday that if it is confirmed a Malaysian airliner was shot down over Ukraine, those responsible "must be brought to account."

Malaysia Airlines flight MH17 was flying from Amsterdam to Kuala Lumpur when it crashed on Thursday, killing all 298 people on board including nine Britons.

Russia warned Friday it may respond if cross-border shooting from Ukraine continues, sharply raising tensions over the crisis a day after a Malaysian jet crashed in the country's rebel-held east killing all 298 people aboard.

"We already warned that if this continues then we will take measures. At least if it is clear that this has been done deliberately I am convinced that such a firing position should be neutralized as a one-off measure," Russian Foreign Minister Sergei Lavrov told Rossiya 24 state television.

Palestinian President Mahmoud Abbas reached out for French help Friday to lobby Hamas' regional allies to influence it into accepting a truce with Israel, French Foreign Minister Laurent Fabius said.

Egypt-mediated talks to end the escalating Gaza Strip war have faltered, with Hamas insisting on a comprehensive ceasefire that would end the Israeli blockade of the coastal enclave, Palestinian officials said.

Russia's state-controlled television on Friday wheeled out conspiracy theories to explain the Malaysian air crash including one holding that it was a bungled attempt to down President Vladimir Putin's presidential jet.

After Putin said that Ukraine was responsible for the crash, Russian state television focused on several theories that pinned the blame accordingly. 

President Barack Obama said Thursday the crash of a Malaysian airliner in eastern Ukraine was a "terrible tragedy" and said U.S. officials were trying to establish if any Americans were on board, as the UK expressed “shock” and France urged an immediate probe.

"The world is watching reports of a downed passenger jet near the Russia/Ukraine border. And it looks like it may be a terrible tragedy," Obama said, before going ahead with a previously scheduled event in Wilmington, Delaware.

President Barack Obama and Russian President Vladimir Putin spoke by phone on Thursday about tough new sanctions imposed on Moscow on Ukraine.

White House spokesman Josh Earnest did not divulge other topics of the conversation. The Kremlin however said that the two leaders discussed the reported crash of a Malaysian airliner in eastern Ukraine.