SEOUL -- The United States and other members of the Group of Seven will impose new sanctions against Russia as early as Monday because it continues to support separatist actions in Ukraine, White House officials said Saturday.

President Obama, traveling through Asia, has been consulting with U.S. allies about the worsening situation in Ukraine, where a peace agreement struck a week ago has yet to defuse tensions. On Friday, Obama spoke with French President Francois Hollande, German Chancellor Angela Merkel, Italian Prime Minister Matteo Renzi and British Prime Minister David Cameron about the crisis in eastern Ukraine.

The Pentagon said late Friday that Russian aircraft had entered Ukrainian airspace “on several occasions in the last 24 hours” and called on Moscow to take “immediate steps” to defuse the situation.

In a statement released Saturday morning, the members of the G-7 accused Russia of failing to deliver on its part of the accord brokered earlier this month in Geneva.

"We reiterate our strong condemnation of Russia's illegal attempt to annex Crimea and Sevastopol, which we do not recognize.  We will now follow through on the full legal and practical consequences of this illegal annexation, including but not limited to the economic, trade and financial areas," the statement read.

"We have now agreed that we will move swiftly to impose additional sanctions on Russia.  Given the urgency of securing the opportunity for a successful and peaceful democratic vote next month in Ukraine's presidential elections, we have committed to act urgently to intensify targeted sanctions and measures to increase the costs of Russia's actions," it added.

Ben Rhodes, the administration's deputy national security adviser for strategic communications, told reporters on Air Force One that G-7 leaders have agreed there must be further sanctions against Russia but that each country will determine which sanctions they will impose. The sanctions will be coordinated, but not necessarily identical.

"We have discussed with our partners the types of sanctions targets that we’re considering. They have discussed with us the types of targets that they’re considering," Rhodes said. "So we believe that it’s important to move quickly, so I would expect to see movement at the beginning of -- well, I’d say early in the coming week."

A senior U.S. administration official told reporters on background that "U.S. sanctions could come as early as Monday."

Rhodes said new sanctions could target prominent business people and that bringing some pressure to bear on "cronies" would affect the Russian economy.

"So I think it’s important to note that when you sanction just officials, that has one consequence. But when you start to get at the cronies, the individuals who, frankly, control large parts of the Russian economy and some of the entities under their control, you are imposing a significant economic impact beyond simply sanctioning an individual," Rhodes told reporters on Air Force One. "Those are the types of targets that the second executive order that the president signed that allows us to go after these so-called cronies. Those are the types of targets that we are looking at, among others."

Rhodes said U.S. officials "understand there is unease about the economic consequences of sanctions on a large economy like Russia" among Europe's business community, but he also warned that if Russian troops currently massed on the border invade Ukraine, broader sanctions will follow that will have an impact on the international economy.

"Yes, I think that everybody understands that if we see Russians troops that are massed on the border invade Ukraine, that sectoral sanctions will be a necessary response -- even though they will carry with it uncertainty for the global economy, difficulty for each of the countries of the G-7 in its own way, given their various commercial relationships with Russia," Rhodes said. "But the G-7 has resolved that that has to be available and exercised as a cost on Russia if we see further escalation."

The G-7 leaders -- who also include Canadian Prime Minister Stephen Harper and Japanese Prime Minister Shinzo Abe -- and the presidents of the European Council and European Commission said they join together "in expressing our deep concern at the continued efforts by separatists backed by Russia to destabilize eastern Ukraine and our commitment to taking further steps to ensure a peaceful and stable environment for the May 25 presidential election."

The G-7 leaders held out the prospect of a diplomatic solution, however, saying,  "While we continue to prepare to move to broader, coordinated sanctions, including sectoral measures should circumstances warrant, as we committed to in The Hague on March 24, we underscore that the door remains open to a diplomatic resolution of this crisis, on the basis of the Geneva accord.  We urge Russia to join us in committing to that path."