US Defense Secretary James Mattis called Russia an international menace during a visit to Kyiv on Thursday and said the United States would not accept the annexation of Crimea. But he stopped short of promising lethal arms.

Mattis was in the capital to celebrate Ukraine's Independence Day and discuss the government's ongoing conflict with separatists backed by Russia.

"Have no doubt ... the United States stands with Ukraine," Mattis said at a news conference with President Petro Poroshenko.

"Despite Russia's denials, we know they are seeking to redraw international borders by force," Mattis said. He added that such maneuvers would undermine sovereign European nations and stir tension.

Read more: Could sending lethal weapons to Ukraine bring peace?

Ahead of the visit, Poroshenko and his defense minister, Stepan Poltorak, had expressed optimism that the United States would provide government forces with new weapons to help in their fight against rebels who have occupied large parts of eastern Ukraine.

In particular, Ukraine was hoping that Mattis would offer lethal weaponry such as anti-tank and anti-aircraft weapons to push back against the well-armed separatists.

Standing next to Poroshenko on Thursday, Mattis said the US was committed to helping Ukraine build and modernize its forces - but he made no mention of providing lethal arms.

"From the first day of the Russian aggression, we appealed to all countries of the world to help us in the form of lethal weapons," Poltorak had told journalists in Kyiv on Wednesday. "Only Lithuania has given us such help so far."

"We continue to wait and are ready to receive lethal weapons," Poltorak said. "But it's not our decision: It's that of our partner countries. We very much hope for such support."

Read more: NATO representative in Kyiv: We support Ukraine every day

'No decisions made'

The US military has supported the idea of providing government forces with "defensive" weapons, but President Donald Trump is yet to sign off on the deal, expressing fears that it could escalate the conflict.

On Wednesday the US State Department announced that it was still considering the idea.

"In terms of the weapons program, there have been no decisions made," spokesperson Heather Nauert said in response to questions. "We"re not going to rule it in; we’re not going to rule that out right now."

US Vice President Mike Pence recently visited eastern European allies to pledge support as Russia's military maneuvers continue. As part of that tour Pence said he was considering deploying Patriot surface-to-air missiles, a move welcomed by the Baltic states.

A Hitler comparison

In a fiery Independence Day speech on Thursday, Poroshenko denounced Russia as an occupier and compared the country to Nazi Germany.

"With particular pain we remember the heroes of Ilovaisk," Poroshenko said, referencing a battle three years ago in Donetsk. "They were insidiously attacked by regular units of the Russian army that invaded our land without declaring war - as Hitler once did."

Poroshenko said there were more than 3,000 Russian troops on Ukrainian soil and blamed the Kremlin for the deaths of the over 10,000 people killed in the conflict.

"Do not ever forget nor forgive," Poroshenko said.

The defense ministers of Poland, Lithuania, Latvia, Estonia, Montenegro, Moldova and Georgia were also in Kyiv for the 26th anniversary of Ukraine's independence from the Soviet Union.

However, celebrations in the capital were marred after two people were injured in an explosion near the Ukrainian parliament. Police said the blast was likely set off by hooligans.

Ceasefire announced

Separatists in eastern Ukraine have announced that a fresh ceasefire would come into force on Friday as the new school year begins.

The truce - negotiated at a meeting of the Contact Group for Ukraine, made up of representatives from Kyiv, Moscow and the Organization for Security and Co-operation in Europe (OSCE) - would extend an existing ceasefire.

Read more: European and Russian leaders agree new ceasefire deal in Ukraine

In a statement released on Thursday, the OSCE, which has a monitoring mission in eastern Ukraine, welcomed "the recommitment to ceasefire," calling it "an encouraging joint, political signal from all signatories" to the peace plan.

No end date for the ceasefire was given.

aw/mkg (dpa, AFP)