By YURAS KARMANAU and PETER LEONARD
DONETSK, Ukraine (AP) -- Ukraine's government took an increasingly aggressive stance Tuesday toward the pro-Russia separatists, vowing to expunge them from their reduced area of control and imposing new conditions before peace talks can restart.
But as the military moves to encircle the rebel-held territory in eastern Ukraine, the government also said it would stop using the air and artillery strikes that drove the rebels from other towns so as to avoid terrorizing civilians.
Ukraine has displayed growing confidence in recent days after driving the insurgents from Slovyansk, a city that had been the heart of the armed resistance since mid-April. Security officials said Tuesday the area held by the rebels has now been reduced by half.
This apparent rout has forced hundreds of militants to regroup in Donetsk, the regional capital, where they occupy government buildings and move freely around the city.
Andrei Purgin, deputy prime minister of the self-proclaimed independent Donetsk People's Republic, said the rebels have an estimated 15,000 fighters and are focusing their efforts on defending Donetsk, a major industrial hub of 1 million.
"We are creating one DPR fist that is ready to fight and repel the Ukrainian army," Purgin told The Associated Press.
He said his forces control all of Donetsk, where the normally busy streets were largely vacant but for groups of automatic rifle-toting rebels on patrol.
"After Slovyansk we are gathering strength and resting. In Donetsk, we feel at home, and a home must be defended and protected," said one 27-year-old rebel fighter, who gave his name only as Dmitry for fear of retaliation. He was patrolling a central district along with seven other militia members.
A major asset still under government control is the Donetsk Airport, the scene of a bloody clash in May that claimed the lives of dozens of insurgents. Purgin vowed that the rebels would soon take "all assets of interest, including the airport."
Donetsk Mayor Alexander Lukyanchenko, who has cautiously refrained from openly taking sides in the conflict, said he was assured by Ukraine's president that the military will not launch air and artillery strikes on the city.
Those strikes had hit Slovyansk and other rebel-held towns to vocal criticism from Russia, which accused the central government in Kiev of indiscriminately killing civilians.
More than 400 people have died and tens of thousands have fled their homes during the nearly three-monthlong standoff between the rebels and the new government in Kiev, which came to power after the previous Russia-friendly president was ousted in February.
National Security Council spokesman Andrei Lysenko said Tuesday that plans were being drawn up to recapture Donetsk, as well as another insurgent-held city, Luhansk, without the use of artillery or aviation. He said Monday that the military would create cordons around the two cities to try to cut off rebel supply lines.
In Luhansk, an apartment building and a business center were shelled on Tuesday, but no injuries were reported. The circumstances of the shelling were not immediately clear.
In Donetsk, tension was high among residents who watched with dismay as Slovyansk, about 110 kilometers (65 miles) to the north, fell in an increasingly ugly standoff.
"I plan to leave the city as soon as possible," said Yekaterina Kachan, 47, who said the restaurant where she works was robbed by militia fighters. "They have turned us all into hostages, but I have no intention of digging graves for separatists under the muzzle of a rifle."
Rebels in Ukraine and nationalists in Russia have called for the Kremlin to protect the insurgents, but Russian President Vladimir Putin has so far made no comment on their defeat in Slovyansk.
Putin may be wary of more sanctions being imposed by the West, which slapped visa bans and asset freezes on Russian officials and members of Putin's inner circle after Russia annexed the Black Sea region of Crimea in March.
Kiev has accused Russia of lending direct support to the insurgents, something which Moscow denies.
Purgin admitted to feeling disappointed by Russia.
"We don't understand the position of the Russian leadership," he said. "We do, however, feel colossal support from Russian society."
Russian state media have been stark in their criticism of Ukraine and cast the rebel campaign as a fight for liberation from a zealous nationalist government. But they have recently moderated their rhetoric.
Broadcasts on civilian victims of Ukrainian military operations have been ubiquitous in Russia, but Kremlin-controlled television stations have downplayed the significance of losing Slovyansk last weekend, reassuring viewers that the rebels are equipped well enough to repel any moves on Donetsk. There appears little interest in Moscow in building public support for a Russian military intervention in Ukraine.
A 10-day cease-fire that ended in late June was punctuated by frequent clashes and produced no progress in reaching a negotiated settlement.
In an indication of Kiev's increasingly intransigent line, Defense Minister Valery Heletey said Tuesday that cease-fire negotiations could only be restarted once the rebels lay down their weapons - something the rebels have rejected. Equally unacceptable to the rebels was President Petro Poroshenko's suggestion that mediation take place in Svyatogorsk, a government-controlled town north of Slovyansk.
"This is a big risk for us. It is possible we could go and then not return from Svyatogorsk," Purgin said. "But we are not opposed to the idea of consultations itself."
Leonard reported from Kiev, Ukraine. Balint Szlanko in Luhansk and Laura Mills in Moscow also contributed to this report.