Russia has agreed to supply Iran with advanced S-300 anti-aircraft missiles and build an additional nuclear reactor at the Bushehr nuclear site. The Russian Kommersant daily reported on Wednesday, amid increased international pressure against the two countries' mutual ally Syria.

A "source close to the Kremlin" told the Kommersant that the agreements would be discussed during Russian President Vladimir Putin's visit to Teheran on Friday. Putin is set to meet with high-ranking Iranian officials, including President Hassan Rohani.

During a debate Wednesday in the Russian parliament of a draft resolution on Syria, Alexei Pushkov, the Kremlin-connected chief of the foreign affairs committee in the lower house of parliament, told lawmakers that Russia could expand arms sales to Iran and revise the terms of U.S.­ military transit to Afghanistan if Washington launches a strike on Syria.

Pushkov said such action now would be premature as Russia and the U.S. are working to find a diplomatic solution to the crisis, but he warned that if the "party of war" prevails in Washington, Russia should consider those moves.

"If the U.S. takes the path of exacerbating the situation and forgoing diplomacy for the sake of a military scenario, such measures would seem absolutely justified to me," Pushkov said.

He also said that Moscow hopes that the U.S. will back Russia's proposal for Syria to put its chemical weapons under international control for their subsequent dismantling.

Iran's supreme leader, Ayatollah Ali Khamenei, said on Wednesday he hoped that a U.S. promise to pursue diplomacy to remove the threat of chemical weapons in Syria was "serious," the Iranian state news agency IRNA reported.

"I am hopeful that the United States new attitude to Syria is serious and not a game with the media. For weeks they have threatened war against the people of this region for the benefit of the Zionists ]Israel]," Khameini said during a public address.

According to the report in Kommersant, Putin reached a decision last weekend to end the ongoing controversy over the sale of S-300 missiles to Iran by finalizing the deal, on condition that Teheran drop a $4 billion lawsuit against Rosoboronexport, the state intermediary that oversees Russian defense imports and exports.

The lawsuit was filed by Iran after Russia canceled a contract for the missiles originally signed in 2007. The report indicated that the contract was canceled in 2010 due to pressure from Israel.

Earlier this year, the possible sale of Russian S-300 missiles to beleaguered Syrian President Bashar Assad caused controversy in the international community as well, and Israel staunchly opposed such a move, fearing that the advanced missiles could fall into the hands of Hezbollah, in Lebanon.

The S-300 system is considered one of the world's most advanced aerial defense systems. Apart for the system's advanced radar, which can identify and track long-range targets, the missile themselves have a range of 200 kilometers.

Because of the system's advanced technology, the time required to make it operational can range between three to six months.

Israeli Prime Minister Benjamin Netanyahu discussed the issue with European foreign ministers in May. "If the missiles are provided and become operational Israel's entire airspace will become a no-fly zone," Netanyahu told the European foreign ministers. "The missile transfer is a significant security challenge to Israel and we will not be able to stand idly by."

In June, Russian Foreign Minister Sergey Lavrov said that his nation would honor its controversial contract to deliver the S-300 systems to Syria, but that the order has yet to be filled.

"We respect all our contracts and are honoring all our contractual obligations," said Lavrov said in an interview with Russian state TV.

"As yet, the contracts are not finished, they have not been delivered in full," he added.

According to foreign media reports, Israel was responsible for three airstrikes on Syrian territory, each one targeting advanced weapons systems believed to be en route to Hezbollah in southern Lebanon.

In early May, two alleged strikes targeted shipments of Iranian Fateh-100 missile en route to Hezbollah. These missiles are said to be extremely accurate, with a range of up to 300 kilometers.

Reports indicated that Israel also attacked a convoy carrying anti-aircraft missiles in January as well.