#Poroshenko's 14-point peace plan leaked today and @alexmazuka got a hold of it: https://t.co/cAerR7plou #Ukraine pic.twitter.com/McyapNL5Oq
— Christopher Miller (@ChristopherJM) June 19, 2014
#Poroshenko's peace plan includes amnesty, disarmament, release of hostages, buffer zone at Rus border, protection of Rus lang, local elex
— Myroslava Petsa (@myroslavapetsa) June 19, 2014
Reports said the fighting appeared to be centered around the villages of Krasny Liman and nearby Yampil in the region of Donetsk.
One military source quoted by the Reuters news agency said some 4,000 separatists had been involved while Ukrainian infantry were supported by some 20 tanks as well as artillery and heavy armor.
A top rebel commander, Igor Strelkov, reported "heavy losses" in equipment and arms among the separatists.
There was no word on casualties from the government side.
Fighting reportedly erupted early on June 19 after rebels refused to lay down their arms as part of President Petro Poroshenko's proposed peace plan.
It includes an offer of a unilateral cease-fire by government forces and amnesty for the separatists - but only if they lay down their weapons.
On his website, Poroshenko said he outlined the plan to Russian President Vladimir Putin by phone on June 19, highlighting the need for hostages to be freed and "an effective regime of control" established on the joint border.
Poroshenko also said he expressed hope Putin would support the plan and any cease-fire that would be declared.
The two leaders spoke hours after NATO Secretary-General Anders Fogh Rasmussen said that at least a few thousand more Russian troops were now on Ukraine's long eastern border.
Kyiv has accused Russia of stirring up the unrest and of allowing volunteer fighters from Russia to cross into Ukraine to support the rebels.
This is denied by Moscow, which has been urging Poroshenko to end "punitive action" against the rebels.
U.S. Vice President Joe Biden assured Poroshenko late on June 18 that there would be "further costs on Russia" unless it used its influence to stop the separatist violence.
In Kyiv, Poroshenko received a boost when parliament overwhelmingly endorsed his nominations for three key posts including that of foreign minister.
Speaking to journalists later, he said he himself would sign an association agreement with the European Union on June 27 which commentators say will decisively shift Ukraine away from Russia's influence and rule out its joining a Moscow-led customs union.
Vox Pop: What's your attitude towards ex-Foreign Minister Deshchytsia calling Putin "khuilo"? http://t.co/GIzVJYwSSI pic.twitter.com/jOIvabKjIa
— Kyiv Post (@KyivPost) June 20, 2014
Vladimir Putin had a telephone conversation with #Ukraine President Poroshenko on the Ukrainian side’s initiative http://t.co/HwfkI37Wpo
— MFA Russia (@mfa_russia) June 20, 2014
Separatists near #Luhansk tell me they don't trust Poroshenko's ceasefire. Video: http://t.co/qIfxK1c5KL #Ukraine
— Paul Brennan (@paulrbrennan) June 20, 2014
Seven Ukrainian servicemen killed, 30 injured in Yampil, Zakotne area http://t.co/Mth0Q4iJU3 pic.twitter.com/rpU5oh776Y
— Kyiv Post (@KyivPost) June 20, 2014
Luhansk airport comes under fire, militants' combat vehicles enter Luhansk http://t.co/jmoarJ1wUL
— Kyiv Post (@KyivPost) June 20, 2014
More RUS manpads for E Ukraine.Fresh pics from Donetsk oblast http://t.co/7APoEa4BoM Heavy casualties on pro-RUS camp pic.twitter.com/VXebWYO45W
— Ryskeldi Satke (@RyskeldiSatke) June 20, 2014