Ukrainian President Petro Poroshenko has said Ukraine must be ready to defend itself if the peace process with the pro-Russian rebels fails but stressed that the conflict in eastern Ukraine cannot be solved militarily.
Speaking to Ukrainian media on September 21, Poroshenko also said Ukraine had lost 65 percent of its military hardware on the front line during fighting in the Donetsk and Luhansk regions.
Kyiv and the pro-Russian rebels agreed a cease-fire on September 5.
Despite numerous violations, the warring sides agreed on September 19 to withdraw artillery and other heavy weapons to the outer limits of a 30-kilometer buffer zone.
Poroshenko has also put forward a plan, passed by parliament, to grant limited self-rule to the rebels in Donetsk and Luhansk.
However, the Ukrainian military said on September 21 it would not go ahead with setting up the proposed buffer zone after accusing the rebels and Russian troops of continuing to shoot at government forces.
Moscow denies sending forces into Ukraine.
In his question-and-answer session with Ukrainian journalists, Poroshenko suggested it was futile to send more troops to fight the rebels in eastern Ukraine.
"The more Ukrainian army battalions or brigades are brought up, the more troops there are from the Russian Federation," Poroshenko said.
Poroshenko has been criticized at home by pro-Western politicians over his plan, which gives the separatists in Donetsk and Luhansk region limited self-rule for three years, plus an amnesty for separatists fighting government forces.
But Poroshenko said his plan had allowed an exchange of prisoners and the return home of Ukrainian prisoners "who had been undergoing torture."
Later, Poroshenko tweeted that 28 Ukrainian soldiers had been freed on September 21, bringing to 63 the number returned home under a prisoner exchange over two days.
Poroshenko adressed the Congress and met President Barack Obama during a trip to Washington on September 18.
Although Washington turned down Kyiv's request for lethal military hardware, Poroshenko did return home with $53 million in fresh aid and a reported $1 billion in financial guarantees, which could help Ukrainian authorities obtain credits.
Poroshenko said on September 21 that Kyiv expected to receive intelligence equipment, radar, and observation systems "which will allow us to increase ten-fold the effectiveness of our weapons."
Earlier, military spokesman Andriy Lysenko accused separatists and Russian troops of violating the September 5 cease-fire.
He said separatists had carried out a fresh attack on the government-held airport in Donetsk, the east's main industrial hub.
The rebels hold the city of Donetsk.
Lysenko said 40 separatists had been killed in "defensive" fire by Ukrainian forces.
That figure could not be independently confirmed.
Lysenko also said two more Ukrainian soldiers had been killed and eight wounded over the last 24 hours.
Lysenko said work on establishing the buffer zone could not start while the cease-fire was being violated.
With reporting by AFP, Interfax, and Unian