The Ukrainian authorities have said they will end the occupation of administrative buildings by pro-Russian separatists in the east of the country, either by negotiations or force, within 48 hours, as four-way talks between Russia, Ukraine, the US and the EU were announced for next week in an attempt to defuse the tense situation.

"A resolution to this crisis will be found within the next 48 hours," said the interior minister, Arsen Avakov, in Kiev, referring to the eastern cities of Luhansk and Donetsk where protesters remained in control of government buildings.

"For those who want dialogue, we propose talks and a political solution. For the minority who want conflict, they will get a forceful answer from the Ukrainian authorities," he said.

In Luhansk, the protesters did not appear in the mood to compromise, and on Wednesday they were reinforcing the barricades around the security services building they have seized and preparing petrol bombs.

In Donetsk, protesters remain in control of the local administration building, from where on Monday they proclaimed Donetsk an independent republic and said they would hold a referendum within a month on the region's status and whether it should appeal to join Russia.

In Kharkiv, protesters also seized the local administration building, but they were removed by security forces, who arrested 70 people.

Kiev has claimed the protesters are directed by Russian security services, and on Tuesday, the US secretary of state, John Kerry, accused Moscow of stirring up unrest, possibly as a pretext for a Crimea-style military intervention.

Many locals in eastern Ukraine have concerns about the new government in Kiev, but unlike in Crimea support for actually joining Russia is not widespread.

In Moscow, President Vladimir Putin appeared in little mood for negotiation, threatening in a cabinet meeting to demand that Ukraine pay for its gas in advance – a move he said would "correspond with the contract" between Ukraine and Russia.

The Russian gas monopoly, Gazprom, says Russia has not received any money for March gas deliveries and still has a $2.2bn (£1.3bn) debt outstanding from Ukraine. Kiev has said it will pay the debt but has protested at an 80% rise in gas prices announced last week.

Diplomats will hope that four-way talks next week could help to defuse the situation. The talks, planned for an unspecified time and location, will be the first four-way talks since former Ukraine president Viktor Yanukovych fled Ukraine and the new government was formed. Since then, Russia has annexed Crimea, and Kiev and Moscow have been engaged in a bitter war of words, with both sides accusing the other of sponsoring terrorism.

The Kiev government claimed it had evidence that Russian security services were behind the violence that left more than 100 people dead in Kiev in February, while Russian security services say they have arrested a number of Ukrainians acting on official orders and planning terror attacks inside Russia.