The trial of all-girl punk band Pussy Riot, who performed a song criticizing President Vladimir Putin in Moscow's biggest church, resumed Monday with sentencing expected as early as this week.

Western diplomats squeezed into the courtroom as day six of the trial got underway, with Nadezhda Tolokonnikova, Maria Alyokhina and Yekaterina Samutsevich sitting inside a glass enclosure reserved for defendants.

President Vladimir Putin will strongly defend Russia's position on the Syria conflict when he meets British Prime Minister David Cameron in London on Thursday, his spokesman said.

"We expect to have another opportunity to continue our dialogue and explain to the British side our well-argued, consistent and absolutely clear position on the (Syria) problem," spokesman Dmitry Peskov told Russian news agencies.

Russian authorities said Thursday they had detained two more people in a probe into clashes between the opposition and police on the eve of Vladimir Putin's inauguration for a third term in May.

Russia's Investigative Committee said two more activists, identified as Nikolai Kavkazsky and Alexei Polikhovich, had been detained as part of the probe into the May 6 violence.

Russian President Vladimir Putin warned on Monday of a protracted civil war in Syria should President Bashar Assad be "unconstitutionally" removed from power by rebel fighters.

"We are afraid that if the country's current leadership is removed from power unconstitutionally, then the opposition and today's leadership may simply change places," Russian news agencies quoted Putin as saying.

Russian President Vladimir Putin has signed into law a controversial bill passed by parliament that brands NGOs who receive funding from abroad as "foreign agents", the Kremlin said Saturday.

The law, which has caused huge concern among activists who fear it will be used to stigmatize critical NGOs, was signed by Putin after it was rushed through the lower and upper houses of parliament before their summer breaks.

Russian President Vladimir Putin warned Western powers on Friday not to take unilateral action against the Syrian government outside the U.N. Security Council.

The Kremlin said Putin delivered the comments at a closed meeting of Russia's powerful Security Council that groups all the top ministers and decides strategy on the most sensitive foreign and domestic affairs.

Russian President Vladimir Putin told visiting Syria peace mediator Kofi Annan on Tuesday that he would "do everything" to support the U.N.-Arab League envoy's plan to end the conflict.

"From the very start, from the first steps, we supported and continue to support your efforts aimed at restoring civil peace," Putin told Annan at the start of their Kremlin meeting.

Syrian peace mediator Kofi Annan was due in Moscow on Monday for talks with President Vladimir Putin that come amid growing pressure on Russia to finally back the ouster of President Bashar Assad.

The Kremlin said Sunday the U.N.-Arab League envoy would arrive in Moscow on Monday and meet Putin the following day for talks in which "Russia will underscore its support the peace plan of Kofi Annan."

Turkish Prime Minister Recep Tayyip Erdogan leaves for Russia next Wednesday to discuss the developments in Syria with Russian President Vladimir Putin, his office announced Thursday.

"Significant regional and international developments led by Syria are on the table to be discussed thoroughly," during Erdogan's visit, the written statement said.

Russian President Vladimir Putin said on Monday that Syria needed dialogue between the regime and opposition rather than foreign intervention to ensure a lasting peace.