LUHANSK, Ukraine — Pro-Russian insurgents captured three government bases in eastern Ukraine in a series of humiliating defeats for the beleaguered armed forces on Wednesday, as the president-elect promised new initiatives to help end the mutiny in the country's industrial heartland.

Petro Poroshenko, speaking in Warsaw after meeting with U.S. President Barack Obama and other Western leaders, rejected a call from Ukraine's interim authorities to introduce martial law in the restive east, saying he would seek to pacify the region with an offer of amnesty and a promise of early regional elections.

Poroshenko's overture, expected to be detailed in his inaugural address on Saturday, came as the Ukrainian troops suffered a series of embarrassing setbacks.

National Guard forces ran out of ammunition and had to flee their base near the eastern city of Luhansk after hours of battle in which six militants were killed and three Ukrainian soldiers were injured.

The defeat came as rebel forces seized a border guard headquarters on the city's outskirts after besieging it for two days, then forced guards out of another base in the nearby town of Sverdlovsk on the Russian border. The guards there were granted safe passage and left with their weapons.

The setbacks highlighted the ineffectiveness of Ukraine's badly trained and cash-starved armed forces, which also have been plagued by bad communication and poor supply lines.

Ukraine's provisional authorities have blamed the recent military failures on pro-Russia former President Viktor Yanukovych, claiming that his corrupt government starved soldiers of resources and training.

The fund shortage is so desperate that the Defense Ministry had to set up a charity account to support the armed forces while volunteers across the country have been buying provisions for the soldiers.

Obama, in Warsaw for a celebration on the 25th anniversary of Poland's first partially free election, praised Poroshenko for reaching out to the east, while offering $5 million in new aid for Ukraine's military for equipment that could help in the fight against the insurgents.

The White House said the aid would include, for the first time, body armor and night-vision goggles for the use of troops. The United States already has provided meals and money for medical supplies and other non-lethal assistance, including clothing, sleeping bags and generators.

Many Ukrainian units in the east are manned by poorly trained conscripts, who come from the region and appear reluctant to engage the rebels.

The fighting in the east has escalated following the May 25 presidential vote won by Poroshenko, with rebels launching an attack on a major airport, shooting down a government helicopter, and besieging a number of military bases.

Trying to regain the initiative, Ukrainian troops on Tuesday launched an offensive against pro-Russian insurgents in Slovyansk, a city that sits on a strategic highway about 55 miles north of Donetsk, the largest city in the east. Vladislav Seleznyov, a government spokesman for the anti-rebel operation, said two government soldiers were killed and 42 injured in daylong fighting. Seleznyov put the death toll of the rebels at 300, but the insurgents rejected his claim.

In Kiev, Interim President Oleksandr Turchynov — who will hand over to Poroshenko on Saturday — asked Ukraine's Security and Defense Council late Tuesday to consider imposing martial law in parts of eastern Ukraine in a bid to stabilize the situation.

Poroshenko dismissed that idea, saying that it would not serve peace efforts in the east.

Speaking in English, Poroshenko said he will use his inauguration to make a proposal to restore law, order and peace. It would include a wide amnesty, and the "creation of the conditions for early local elections," as part of efforts to reform Ukraine's local administrations.

Poroshenko and Russian President Vladimir Putin will be among many world leaders in France this week to attend events commemorating the 70th anniversary of the Allied invasion of Normandy in World War II.