* U.S.-Russian relations have been strained over Syria
* Kremlin statement upbeat after phone call
* Russia arms official says Syria shipments blocked (Updates with comments from Russian arms trade official)
By Alissa de Carbonnel
MOSCOW, March 1 (Reuters) - Vladimir Putin and Barack Obama have told their foreign ministers to keep in close touch and seek "new initiatives" to end Syria's civil war, the Kremlin said after a telephone conversation between the two leaders.
The Kremlin said Putin and Obama also pledged to avoid steps that would harm Russian-U.S. relations, which have been strained by differences over Syria and other issues including Putin's treatment of opponents since he began a new term as president last May.
The phone call took place three days after Russian Foreign Minister Sergei Lavrov and new U.S. Secretary of State John Kerry discussed the Syrian crisis at a meeting in Berlin but signalled no breakthrough.
"The presidents have instructed (Lavrov and Kerry) to continue active contacts focused on working out possible new initiatives aimed at a political settlement of the crisis (in Syria)," the Kremlin said in a statement.
Senior U.S. and Russian diplomats have met repeatedly in recent months, along with U.N. Syria envoy Lakhdar Brahimi, with little sign of progress toward a solution to the nearly two-year-old conflict that has killed more than 70,000 people.
They have long been at odds over the fate of Syrian President Bashar al-Assad. The United States says he must go but Russia says his exit from power must not be a precondition for a negotiated settlement.
Russia's Foreign Ministry said earlier on Friday that decisions made at a "Friends of Syria" meeting in Rome, after which Kerry pledged increased non-lethal U.S. aid for Syrian rebels, would embolden Assad's foes seeking his overthrow.
Brahimi emphasised on Thursday that Washington and Moscow should play a leading role in seeking a solution, saying: "If Russia and the United States reached a real agreement, it would be easy for an international decision to be taken."
Russia says it is not propping up Assad and has publicly distanced itself from him, but continues to supply arms to the Syrian military. Moscow has lent Assad crucial support by blocking, with China, three U.N. Security Council resolutions aimed to push him out or press him to end the bloodshed.
On Friday a top Russian arms trade official complained that weapons deliveries to Syria had been disrupted.
"We are respecting our contracts with Syria, but a real war has been declared against us - I would say a secret one. Our shipments - both by sea and air - are being detained...our insurance is being cancelled," Alexander Fomin, the head of the Federal Service for Military and Technical Cooperation, told Ekho Moskvy radio.
"This blockade exists, although Russia has not violated any international obligations." He said payments for arms shipments had been frozen by Western financial institutions with losses to Russia of hundreds of millions of dollars.
Despite criticism from Western and Arab powers, Russia says it is not in violation of U.N. Security Council resolutions and weapons sold to Syria include anti-missile air defence systems but no attack weapons such as helicopters.
On Thursday, Putin cautiously welcomed a suggestion from French leader Francois Hollande that dialogue on Syria be broadened to bring in parties that could act as negotiators between Assad and opposition rebels.
Assad's government has shown increased willingness to hold talks with the opposition. Foreign Minister Walid al-Moualem said in Moscow on Monday that the government would even speak to armed rebels.
The Kremlin said the telephone call was initiated by Obama, and the statement sounded an upbeat note on Russian-U.S. ties.
"The leaders of both countries are united in their desire to avoid any steps that could negatively reflect on bilateral relations," it said.
Already strained by what Kremlin critics say is a crackdown on dissent, ties worsened after Obama signed a law in December aimed at punishing suspected Russian human rights abusers by barring them from the United States and freezing their assets there.
Putin responded with a law imposing similar measures and banning the adoption of Russian children by Americans. (Reporting By Alissa de Carbonnel; Editing by Steve Gutterman and Rosalind Russell)