Russia is building an airstrip in the Syrian regime's stronghold Latakia province, and has brought hundreds of technicians and military advisers to the site, a monitor said Sunday.

The claim comes as Washington accuses Moscow of a military build-up in Syria, where Russia has backed President Bashar Assad's regime against an uprising of more than four years.

As Russians voted in local elections on Sunday set to confirm the ruling party's dominance, the opposition reported mass vote rigging and police stormed the office of independent vote monitors.

The local elections across 83 regions were expected to be easily won by the United Russia party which supports President Vladimir Putin.

Progress has been made on some contentious issues in the peace process, the foreign ministers of Germany, Russia, Ukraine and France said after holding talks in Berlin on Saturday to prepare for a summit in Paris on October 2.

Germany's top diplomat, Frank-Walter Steinmeier, said the meeting had been "less confrontational" than previous ones and that the warring sides were now "very close" to an agreement on withdrawing heavy weapons from the frontline.

Two Russian planes carrying humanitarian aid landed in Syria on Saturday, state media said, amid reports that Moscow is beefing up military support to its ally Damascus.

"Two Russian planes arrived today at the Latakia Martyr Bassil al-Assad international airport carrying 80 tonnes of humanitarian aid provided by Russia," state news reported.

Ukrainian Prime Minister Arseniy Yatsenyuk on Saturday urged the West not to lift sanctions on Russia for its role in the Ukraine conflict unless the Minsk peace deal is fully implemented.

His call came ahead of a meeting of the foreign ministers of Germany, Russia, Ukraine and France in Berlin to prepare for a summit to be held in Paris in early October.

Russia has issued an alert for Cyprus to divert aircraft from normal flight paths as it plans to conduct military exercises off the Syria' coast next week, officials on the island said Friday.

Reports in Moscow said Russia had sent NOTAMs (Notice to Airmen) to the U.S. Federal Aviation Administration about the exercises between the Syrian port of Tartus and Cyprus, about 100 kilometers (60 miles) away.

Sweden's foreign ministry on Friday summoned Russia's ambassador after Moscow threatened retaliatory measures if the Scandinavian country joined NATO.

Viktor Tatarintsev "is expected to come today" at Foreign Minister Margot Wallstrom's request, a foreign ministry spokeswoman said.

Russian President Vladimir Putin and Italy's billionaire former leader Silvio Berlusconi on Friday met for informal talks in Crimea which Moscow annexed from Ukraine last year, an official said.

Putin and Italy's disgraced former prime minister, who the Russian strongman counts among his close friends, visited an Italian war cemetery near the Black Sea port of Sevastopol, a spokeswoman for Crimea's regional leader told AFP.

Canada, India, Singapore and Egypt are "seriously" interested in buying France's two Mistral warships, a senior official has said, after Paris scrapped a deal to sell the vessels to Russia over the Ukraine crisis.

Louis Gautier, an official who advises the prime minister on defense and security matters, also told lawmakers this week that the cost of abandoning the agreement with Russia would be at least 1.1 billion euros ($1.2 billion) if the government did not find another buyer, according to a summary of his comments obtained by AFP Friday.

Russia on Friday called for coordination between a U.S.-led coalition and Moscow to avoid "unintended incidents" in Syria where Washington accuses it of expanding its military presence.

In recent days Russia has faced criticism from the United States which says Moscow is ramping up its military presence in Syria in an apparent bid to prop up President Bashar Assad.