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Russia Sends Attack Helicopters to Syria, U.S. Official Says

The Pentagon said they agreed to keep talking.

Four Russian attack helicopters and four Russian transport helicopters have arrived in Syria in the past day, and Russia is also preparing to send attack jets, a senior American defense official told NBC News on Friday.

The disclosure came hours after the top U.S. and Russian defense officials spoke on the phone for the first time in more than a year to talk about the crisis in Syria, where Russia is building a military presence.

Defense Minister Sergey Shoygu told his U.S. counterpart, Defense Secretary Ashton Carter, that the Russian buildup is “defensive in nature,” according to a senior U.S. defense official.

Shoygu also said that the buildup was to honor Russian commitments to the Syrian government, the official said. The official refused to speculate that those commitments might include Russian military support and protection of the regime of Syrian President Bashar Assad.

Russian military support for the Assad government, which U.S. military officials say would probably include airstrikes against Syrian rebels attempting to overthrow the regime, would create a dilemma for the Obama administration. President Obama has long stressed that the Assad regime “must go.”

The Pentagon described the conversation between Carter and Shoygu as constructive and said they agreed to keep talking. They talked about ways to de-escalate the conflict in Syria and fight ISIS, the Pentagon said.

Satellite imagery on Thursday showed the recent arrival of Russian tanks and other military equipment at an air base in the Latakia coastal region of Syria. The Pentagon said on Monday that it had seen a “continued steady flow” of equipment and people for more than a week.

The eight helicopters that have arrived in the past day are based just outside Latakia, the official said.

Related: Russia to U.S.: Talk to Us on Syria or Risk 'Unintended Incidents'

Russia supports the Assad government, while the United States supports the insurgents fighting him in a bloody four-year civil war.

The United States suspended talks between its military and the Russian military last year, after Russia seized the Crimean peninsula from Ukraine.