Petro Poroshenko is clearly anxious. That much is evident from the Ukrainian president's hastily issued invitation asking G7 ambassadors to attend talks next Thursday. On the agenda? The state of the Ukrainian government, said Jan Tombinski, the EU's representative in Ukraine.

The talks follow the surprise resignation of Economics Minister Aivaras Abromavicius on Wednesday. He explained his decision, saying that he and his ministry were under pressure from several politicians from the president's party.

"My team and I don't want to be puppets for covert corruption," he said.

He was also ready to name names: Ihor Kononenko, deputy parliamentary group chairman for the president's party, businessman, and one of Poroshenko's closest allies. Abromavicius accused him, among other things, of favoritism when handing out lucrative positions in state companies in the chemicals and metals industries.

Kononenko denies the charges. The case is now being investigated by the anti-corruption office, which was established last year.

Ambassadors praise economics minister

Poroshenko on Wednesday called on his economics minister to remain in the government, but Abromavicius could not be convinced. He had already cleaned out his office and taken his personal belongings with him, according to reports in the Ukrainian media. Officially, parliament still has to vote on his resignation, and it's not yet clear what the result will be. Several of his more senior colleagues also tendered their resignations.

Better days: Yatsenyuk (l.) and Poroshenko during the inauguration of parliament in November 2014

The unusually swift reaction from Western ambassadors, Germany's included, shows just how serious the situation is.

Just hours after Abromavicius' resignation, they issued a short statement of regret for the loss of an economics minister who "had shown real results in terms of reform for Ukraine."

They praised his service in stabilizing the hard-hit, crisis-ridden Ukrainian economy and his commitment to fighting corruption and increasing transparency. The ambassadors called on the Ukrainian leadership to put aside their differences.

Western help for Ukraine?

Abromavicius is one of the key ministers in Prime Minister Arseni Yatsenyuk's government. The 40-year-old native of Lithuania is one of originally three non-Ukrainian ministers who have been in office for around a year. Among other things, he was responsible for crafting the conditions for billions in loans from the International Monetary Fund (IMF). Ukraine needs the money to fend off the constant threat of bankruptcy.

Some experts say Ukraine's financial aid is now in danger.

"Western partners could present Poroshenko with a political ultimatum," said Hlib Wyschlinski, managing director for the Kyiv Center for Economic Strategy. If the reform process stops, so does the cash flow. "And Ukraine doesn't have any other sources," said Wyschlinski.

German political scientist Andreas Umland, who lives in Kyiv, sees the situation similarly. He does not rule out the possibility that the recent events in Kyiv could spark a bigger political crisis.

Demands for Yatsenyuk's resignation

President Petro Poroshenko and Prime Minister of Ukraine Arseniy Yatsenyuk during the first meeting of the Constitutional Commission

Ukrainian politicians appear to have come to the same conclusion. Parliamentary chairman Wolodymyr Hrojsman recently warned that a "serious political crisis" is in the making. Yatsenyuk said that while he appreciates the opinion of those who have tendered their resignations, stepping down now would be akin to "fleeing the battlefield." He criticized the verbal attacks on his government, and spoke of a power struggle as well as the "dirty realities of politics."

Yatsenyuk is on thin ice at the moment. His party has had single-digit approval ratings for months. Politicians from Poroshenko's party have frequently accused him of corruption and demanded that he step down.

Political observers, such as Serhij Rudenko, see Abromavicius' resignation as a clear indicator of the escalating power struggle between the president and the prime minister. Without Yatsenyuk's faction, there would be no new majority in parliament, and Ukraine would once again be facing early elections.

Many observers in Kyiv are convinced that only outside pressure from the West has so far prevented the government and the parliamentary coalition from falling apart.

Kononenko is taking a leave from his office as the deputy parliamentary group chairman of Poroshenko's party until the corruption charges against him have been investigated. But whether that will help allay the crisis is doubtful. On February 16, the government will address parliament and give a summary of its achievements. Observers are predicting a tumultuous session, and say further resignations - and even a vote of no confidence - cannot be ruled out.