MOSCOW (AP) — Russia on Tuesday argued strongly against Turkey's demand to keep a leading Kurdish group out of Syrian peace talks, and said it expects the U.N. envoy to resist "blackmail" by Turkey and others, reflecting sharp differences that remain ahead of the talks.

Russian Foreign Minister Sergey Lavrov also denied allegations that Moscow had urged Syrian President Bashar Assad to step down and could offer him political asylum.

He specifically shrugged off reports last week claiming that Russia's military intelligence chief had traveled to Damascus to try to persuade Assad to go. Lavrov said there was no point in such a trip as Assad visited Moscow in the fall and had extensive talks with President Vladimir Putin.

"No one has asked for or offered any political asylum," he said, adding that Assad had promised Putin he would sit down for peace talks with opposition, including armed groups, and engage the "patriotic" opposition in the fight against the Islamic State group alongside the Syrian army.

Lavrov emphasized that the Kurdish group, the Democratic Union Party, or PYD, plays an important role in fighting the Islamic State group and is an essential part of political settlement in Syria.

Turkey sees the PYD and its YPG militia group as branches of the Kurdistan Workers' Party, a Kurdish resistance group it has long fought and considers a terrorist group.

Lavrov warned that it would be a "grave mistake" not to invite the PYD. "How can you talk about political reforms in Syria if you ignore a leading Kurdish party?" he said, adding that the Kurds account for 15 percent of the population.

Lavrov also warned against Saudi Arabia's proposal to invite only opposition groups that it hosted at a meeting last month, saying the Syrian peace process should also include other opposition representatives, like those that met for talks in Moscow last year.

The current opposition negotiating team announced in Saudi Arabia last week includes Saudi-backed Islamic rebel factions like Jaish al-Islam, or the Army of Islam, which Russia considers terrorists.

The nearly five-year Syrian conflict that began in 2011 with protests against Assad's rule, has morphed into an all-out war that has killed a quarter-million and displaced millions.

Lavrov's statement at a news conference reflects the tough posturing ahead of Syria peace talks set to start Friday. U.N. special envoy Staffan de Mistura will be sending invitations amid intense jockeying between countries like Russia and Turkey about who should be invited.

Russia, a key ally of Assad, has called for the inclusion of Kurdish representatives, and the U.S. and others have supported the Kurds in the fight against IS. Russia's relations with Turkey are at a freezing point after a Turkish fighter jet downed a Russian warplane at the border with Syria in November.

In Ankara, Turkish Prime Minister Ahmet Davutoglu on Tuesday reiterated Turkey's opposition to including Syrian Kurdish forces at the Geneva talks.

"A table without the Kurds would be incomplete. We do not oppose the Kurds but we oppose the PYD and YPG who oppress the Kurds," Davutoglu said in his weekly address to his party's legislators. "It is not acceptable for us for a terror organization to be included within the opposition."

Foreign minister Mevlut Cavusoglu, in an interview with NTV television, said Turkey would boycott the talks if the PYD were invited.

Lavrov has dismissed the demand by some opposition groups that the Syrian military must lift the siege of some areas before the talks begin, saying that unblocking the besieged areas and delivering humanitarian aid should be an important part of the negotiations.

"There must be no preconditions for starting the talks, and the humanitarian issues must be among the central issues on their agenda," he said, adding that while the plight of the city of Madaya blockaded by Syrian government forces has been widely publicized, a similar situation in government-controlled Deir el-Zour has been largely out of the public eye.