The UN Security Council has called for the "swift deployment" of an international force to Mali.
The call comes after Islamist militants said they had entered the key central town of Konna, advancing further into government-held territory.
The UN has approved plans to send some 3,000 African troops to Mali to recapture the desert north, which is controlled by the militants.
Mali's president has asked the UN and France for help, diplomats say.
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The US ambassador to the UN, Susan Rice, asked whether the Malian President Dioncounda Traore had requested specific kinds of military support, said: "It wasn't specific, but it basically said, 'Help, France!'."
France - the former colonial power - would respond to the request on Friday, France's UN ambassador Gerard Araud said following an emergency meeting of the security council.
For logistical reasons the African force already approved by the UN was not expected to even begin its offensive before September or October, the BBC's Barbara Plett reports from the UN in New York.
The UN resolution also calls for peace talks between the government and rebels, in an attempt to separate them from the foreign extremists, our correspondent reports.
These were set to begin this month but the renewed fighting threatens their chances of success, she adds.
Some European leaders have voiced concerns that jihadists could use Mali's vast Islamist-controlled area to launch attacks on Europe.
The latest fighting is the most serious since the militants captured the north from government forces in April 2012.
A spokesman for the Ansar Dine militant group, Sanda Abu Mohammed, said their fighters had driven out government forces from Konna, about 700km (435 miles) north-east of Bamako.
"We are actually in Konna for the jihad [holy war]," he is quoted by AFP news agency as saying.
The army has not commented on the claim.
The Islamists have been accused of war crimes and attempting to impose a strict version of Sharia, prompting fears the region could become a regional hub for al-Qaeda-linked militancy.
Burkina Faso is trying to mediate an end to the conflict - BBC