MOSCOW (AFP) - US Secretary of State John Kerry on Tuesday sought to narrow differences over the conflict in Syria with President Vladimir Putin, urging the Russian strongman to find common ground to help end the bloodshed.

Mr Kerry is making his first trip to Russia since taking over as the chief US diplomat in February, one of his most diplomatically delicate missions to date.

Washington has long urged Moscow, Syrian President Bashar al-Assad's most powerful ally, to use its sway to halt the bloodshed, accusing Russian leaders of continuing to arm the Syrian regime.

"The United States really believes that we share some very significant common interests with respect to Syria," Mr Kerry told Mr Putin at the start of talks in the Kremlin.

He cited these interests as "stability in the region, not letting extremists create problems in the region and elsewhere."

"It is my hope that today we will be able to dig into that a little bit, and see if we can find common ground." he added.

In his initial remarks, Mr Putin did not specifically address the differences between Washington and Moscow over Syria but said the Kremlin was preparing a response to a message on bilateral ties that President Barack Obama sent in April.

"I think it's very important that our key ministries and institutions, including the foreign ministry, cooperate in finding solutions to the most topical and relevant issues of the day," Mr Putin told Mr Kerry.

"I'm really happy to see you because it offers the chance to discuss in person issues that we believe are difficult," Mr Putin added.

The visit coincides with the first anniversary of Mr Putin's return to the Kremlin for a historic third term on May 7, 2012, which heralded a new chill in relations between Moscow and Washington.

Later, Mr Kerry will also meet Foreign Minister Sergei Lavrov and is expected to hold a news conference.

"I don't know if we will get an agreement or not, but we certainly think it is worth testing and trying to find some ways forward," a senior State Department official said Monday.

Russia has long accused the West of worsening the Syria conflict by seeking to topple the Assad regime, and says Moscow is solely interested in seeing a peaceful solution to a conflict that has claimed more than 70,000 lives in since March 2011.

The US and other Western states have in turn accused Russia of failing to use its influence with the regime to halt the bloodshed and keeping up military deliveries to Mr Assad.

Mr Kerry's visit is taking place at a time of particular tension after Israel launched air strikes in Syria which Israeli sources said targeted Iranian weapons destined for the Lebanese militant group Hezbollah.

The Russian foreign ministry said it was "especially" concerned by the attacks, warning that the violence threatened neighbouring Lebanon.

Turkish Prime Minister Recep Tayyip Erdogan on Tuesday branded Israel's air raids in Syria "unacceptable" but called again on the international community to act over killings by regime forces.

Meanwhile, Iranian Foreign Minister Ali Akbar Salehi, whose country is among Syria's closest allies, is to arrive in Damascus for a previously unannounced visit on Tuesday, an Iranian diplomat said.

Further complicating the picture, UN human rights investigator Carla del Ponte said at the weekend that the rebels may have used the deadly nerve agent sarin.

But a commission of inquiry later said there was no conclusive proof and the United States said it was "highly sceptical".

There are a host of other issues on the agenda of the talks, including last month's Boston Marathon bombings blamed on two brothers of Chechen descent.

More contentious dossiers include American missile defence and rows over a ban by Moscow on American adoptions of Russian children and the Russian authorities' harassment of NGOs.

Mr Kerry is due to meet civil society activists on Wednesday at the residence of Ambassador Michael McFaul at which he will hear their concerns about the lack of democratic progress.

Washington has called for a more open and democratic society, angering Putin and leading him to accuse US-backed non-governmental organisations of actively working against him.