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 President 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 on Wednesday.

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 servicemen 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 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 the anniversary of Poland’s first partially free election, praised Poroshenko while offering $5 million in new aid for Ukraine’s military.