BEIRUT - Syrian President Bashar al-Assad said Thursday he has never faced pressure from Russia to step aside, as US Secretary of State John Kerry headed to Moscow seeking to revive stalled peace efforts.

Speaking to NBC News in Damascus, Assad insisted his Russian counterpart Vladimir Putin and Foreign Minister Sergei Lavrov had never raised the issue of his departure or a political transition.

“Only the Syrian people define who’s going to be the president, when to come, and when to go. They never said a single word regarding this,” he said. Assad’s fate is a key question in efforts to bring about a negotiated settlement to Syria’s five-year civil war. Washington and Moscow have backed a roadmap that calls for a nationwide ceasefire and Geneva-based talks on “political transition.”

Assad said that the US reporter killed in alleged Syrian government bombardment of a rebel district in 2012 was “responsible” for her own death.

Speaking to NBC News in Damascus, Assad said Marie Colvin bore responsibility for her death in the Baba Amr district of Syria’s third city Homs because she had entered the country illegally and worked with “terrorists.”

“It’s a war and she came illegally to Syria. She worked with the terrorists, and because she came illegally, she’s been responsible of everything that befall on her,” Assad said, speaking in English.

In Turkey meanwhile, Prime Minister Binali Yildirim restated his country’s opposition to Assad, saying there could be no solution to the conflict while he was in office. “As long as Assad is there, the problem won’t be solved,” he told the BBC in an interview broadcast late Wednesday.

Syria’s conflict began in 2011 with the brutal repression of anti-government demonstrations and has evolved into a complex multi-front war that has left more than 280,000 dead and forced millions from their homes.

Efforts to bring an end to the war have taken on greater urgency since the emergence of the Islamic State group, which seized control of large parts of Syria and neighbouring Iraq in mid-2014.

The militant group has committed widespread atrocities in areas under its control and organised or inspired a wave of attacks across the Middle East and in Western cities. A US-led coalition is carrying out air strikes against the militants in Syria and Iraq and recent months have seen IS lose significant territory.

The Washington Post reported Thursday that Washington was to offer to cooperate with Russia in joint military action against IS and the Syrian branch of Al-Qaeda, Al-Nusra Front.

In Paris before heading to Moscow, Kerry did not deny the report, but refused to discuss the proposal in detail until he had been to the Kremlin. Kremlin spokesman Dmitry Peskov declined to comment on the report before Moscow had received Washington’s proposal.

According to the Post, which cited sections of what it said was a draft agreement, US and Russian commanders would set up a joint command and control centre to direct intensified air strikes against the groups. Saudi Arabia warned Thursday that any military cooperation between the United States and Russia in Syria must help advance a political transition to end the war without Bashar al-Assad in power.

Foreign Minister Adel al-Jubeir told reporters he was ready to welcome US-Russian cooperation as US Secretary of State John Kerry headed to Moscow for talks on ending Syria’s five-year war.

“With regards to the Russian-American cooperation in the fight against terrorism: this is something we had asked for,” Jubeir told reporters following meetings at the United Nations. But he added: “The key is really to move the situation in Syria along a political process.”

The Washington Post reported that Kerry will propose setting up a joint command and control center to direct air strikes against the Islamic State and other jihadist groups, during his talks with President Vladimir Putin.

The Saudi foreign minister said Syria must move forward on a political transition that provides for an interim governing council with full power to manage state affairs and “lead to a new Syria without Bashar al-Assad in it.”

“Anything that helps move the process in that direction is something that we would welcome,” he added.

Russia had repeatedly called on the United States and other countries to cooperate more closely to defeat the Islamic State group and other jihadists in Syria.

Cooperation with Moscow has long been viewed with suspicion, as it would amount to acceptance of Russia’s backing for the Assad regime.

Saudi Arabia is supporting various rebel groups fighting the Damascus regime, some of whom have close ties with the Al-Qaeda-affiliated Al-Nusra Front and are not considered moderates.

Under a UN plan, the political transition in Syria is to begin on August 1, with the formation of an interim body followed by the drafting of a new constitution and elections 18 months later.

But the fate of Assad remains unresolved, with the opposition demanding that he must leave power immediately.

Such a deal is likely to face criticism that it amounts to a tacit acceptance of Putin’s efforts to shore up Assad’s regime.

In his interview with NBC, Assad also said a US reporter killed in alleged Syrian government bombardment in 2012 was responsible for her own death.

Marie Colvin, a 56-year-old war correspondent working for British newspaper The Sunday Times, died in the rebel-held Baba Amr district of Syria’s third city Homs. “It’s a war and she came illegally to Syria. She worked with the terrorists, and because she came illegally, she’s been responsible of everything that befall on her,” Assad said, speaking in English.

Asked if she was responsible for her own death, Assad replied “of course,” though he denied that his forces had targeted her.

His comments came days after relatives of Colvin filed a lawsuit in a US court alleging Assad’s regime targeted her to stop her covering government atrocities.

The suit, based on information from captured government documents as well as defectors, claims the Syrian military intercepted Colvin’s communications and unleashed a barrage of rocket fire on her location, killing her and French photographer Remi Ochlik.

Russia has conducted more than 50 air strikes since Tuesday against Islamic State (IS) militants near the Syrian city of Palmyra, the defence ministry in Moscow said.

“The Russian air force has increased the intensity of its strikes against targets of the armed units of international terrorist organisations near the city of Palmyra,” the ministry said in a statement Thursday on its Facebook page.

“Since July 12, Russian air force planes have conducted more than 50 strikes against Islamic State personnel and material in this area.”

Six Tupolev bombers flew out of an airbase in Russia on Thursday morning and conducted strikes east of Palmyra, near the cities of Arak and Sukhna, as well as in the Homs region, the statement said.

The ministry said the strikes had destroyed “a command centre, a field camp for IS fighters, two oil processing plants and a large quantity of the enemy’s personnel and military hardware.”

IS fighters were forced out of Palmyra by Syrian regime forces in March with Russian backing, but Arak and Sukhna remain out of the government’s control.

Arak, located 35 kilometres (21 miles) east of Palmyra, is a small town that has strategic importance because of a nearby oil field, while Sukhna, 70 km northeast of Palmyra, is an IS bastion.

Russia is stepping up its bombing campaign in Syria as US Secretary of State John Kerry is set to meet President Vladimir Putin in Moscow on Thursday in Washington’s latest bid to revive the stalled Syrian peace process.

Kerry’s visit to Russia - his second this year - comes as bloodshed continues in defiance of a series of failed ceasefires. Russia and the US appear increasingly at odds over the way forward amid heightened diplomatic tensions.