Updated

Jordan will not take in Syrians fleeing their government's latest offensive in the country's south, officials said Monday, as violence in the Syrian province of Daraa claimed more lives and displaced thousands.

President Bashar Assad's forces have been advancing deeper into Daraa under the cover of Russian airstrikes. The United States has reportedly told rebels not to expect an American intervention to defend them.

The Russian Defense Ministry said Syrian insurgents have attacked 12 areas where rebels shifted alliances and sided with the government. The ministry blamed the attack on al-Qaida-linked fighters, saying it was repelled and that 70 gunmen were killed. It said there were no human losses on the government side.

The statement added that the Russian military will ensure security for three U.N. humanitarian convoys entering the area on Monday.

A war-monitoring group, the Britain-based Syrian Observatory for Human Rights, reported 34 airstrikes in Daraa after midnight Sunday, adding that the shelling reached the contested provincial capital, also called Daraa.

The U.S. State Department said it was "concerned" about the situation in southern Syria and was communicating with parties on the ground, including Russia. The U.S. has called on Moscow to adhere to a de-escalation agreement for the region reached last year. "This is once again an example of Russia flouting arrangements it has entered into with no regard for civilian lives," the statement said.

The U.N. envoy to Syria, Staffan de Mistura, meanwhile held consultations in Geneva with officials from France, Germany, Jordan, Saudi Arabia, Britain and the U.S. on the way ahead on "a Syrian-led and Syrian-owned UN-facilitated Geneva political process in accordance with Security Council resolution."

A statement released by de Mistura's office said the officials discussed the situation on the ground, adding that "grave concerns were expressed at the ongoing military escalation in southwestern Syria" and calls made for an immediate end to the violence.

The city of Daraa is where anti-government protests began in March 2011, inspired by the Arab Spring. The government's violent response to the protests, and the rise of an armed insurgency, tipped the country into a civil war that has so far killed 400,000 and displaced half the population.

The Observatory said 26 civilians have been killed since the government offensive on Daraa began last Tuesday, and more than 17,000 people have fled their homes, moving closer to the Jordanian border.

Jordanian government spokeswoman Jumana Ghunaimat said the kingdom is working with the U.S. and Russia to protect its national interests. The Jordan Times quoted her as saying that Jordan has already absorbed large numbers of Syrian refugees and that "we simply cannot receive more."

Jordan hosts about 660,000 registered refugees, but says the actual number of displaced Syrians in the kingdom is twice as high.

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Associated Press writer Maria Danilova in Moscow contributed.