The U.N. Security Council will vote Saturday on a Western-drafted resolution allowing a ceasefire observer mission in Syria even though Russia's support is in doubt.

The United States called for the vote after a second day of wrangling with Russia over security guarantees for the first 30 unarmed military monitors who U.N.-Arab League envoy Kofi Annan wants in Syria early next week.

Talks between Iran and six world powers in Istanbul on Tehran's nuclear program, the first in 15 months, began Saturday in a "positive atmosphere," a European Union spokesman said.

"There is a positive atmosphere. ... There is a desire for substantive progress," Michael Mann, spokesman for EU foreign policy chief Catherine Ashton, told reporters.

Syrian forces killed six people and shelled rebel areas of Homs on Saturday ahead of a U.N. Security Council vote on a Western-drafted resolution that would send observers to monitor a shaky truce now in its third day.

Forces loyal to President Bashar Assad killed four civilians as they opened fire at a funeral procession of a demonstrator in Aleppo, the Syrian Observatory for Human Rights said.

Western nations and Russia on Friday put forward rival U.N. Security Council resolutions on sending ceasefire observers to Syria as they wrangled over conditions for the mission.

The dispute after two days of tough negotiations means no vote is likely until Saturday on any final resolution which would allow an advance party of 30 unarmed military observers to go to Syria next week.

The United States on Friday called on Iran to show "seriousness" in nuclear talks in Turkey, after Tehran warned it was discouraged by the approach of Western nations.

After a 15-month hiatus, officials from the United States, Russia, China, Britain, France and Germany (known as the P5+1) will meet with Iranian counterparts in Istanbul on Saturday.

Russia will keep a permanent naval presence off Syria's coast to match the growing number of Western warships monitoring the 13-month crisis, a top defense official said on Friday.

"A decision has been taken to keep Russian navy ships permanently stationed near Syria's coast," the RIA Novosti state news agency quoted a senior defense ministry official as saying.

Russia, China and India on Friday jointly called all parties in the standoff over North Korea to show restraint after the reclusive state's failed rocket launch sparked global concern.

"We are convinced that the reaction to these challenges needs to be exclusively diplomatic and political," Lavrov said alongside his Chinese and Indian counterparts after a meeting in Moscow.

North Korea's much-anticipated rocket launch ended quickly in an embarrassing failure early Friday, splintering into pieces over the Yellow Sea soon after takeoff.

Within minutes of the early morning launch, the U.S. and South Korea declared it a failure. North Korea acknowledged that hours later in an announcement broadcast on state TV, saying the satellite had failed to enter into orbit.

The U.N. Security Council could pass a resolution on Friday to allow unarmed observers to go to Syria next week to monitor the fragile ceasefire, diplomats said.

An advanced mission of 20-30 observers could be in place early next week, diplomats said. The full mission would be at least 200 monitors.

Russia called for more time on Thursday for international envoy Kofi Annan's Syrian peace plan to work, as a ceasefire to end months of violence came into force with no major reports of violations.

Foreign Minister Sergei Lavrov said some Arab and Western states had written off Annan's peace plan as a failure even before it had gone into effect and called on them to use their influence with the rebels to avoid future unrest.