A Russian convoy sent into Ukraine in violation of the country鈥檚 borders is the latest act of desperation from Moscow as rebels continue to lose key ground, analysts say.

In what Ukraine is calling a 鈥渄irect invasion,鈥 more than 130 trucks rolled across the border in a rebel-held part of the country Friday. Russia insists the convoy is carrying humanitarian aid, but critics called the move an attempt to arm and support pro-Russian separatists in eastern Ukraine.

The trucks started to return to Russia on Saturday.

The convoy, which had been idling near the border for nearly two weeks, moved just days before Russian President Vladimir Putin and Ukrainian President Petro Poroshenko are scheduled to attend a multilateral summit in Belarus, where top European officials will attempt to de-escalate the situation at the negotiating table.

Mark Stech, executive director of the Canadian Institute of Ukrainian Studies, says the violation of Ukraine鈥檚 borders is a strategic move by Russia to show its teeth ahead of the summit.

鈥淩ussia has had a pattern that before any major international meeting, they would 鈥 escalate their violence in order to be in a position at negotiating table (to) offer to stop that escalation and seem to have compromised something by giving up nothing,鈥 Stech said in an interview on CTV鈥檚 News Channel on Friday.

The hostile move by Russia is a 鈥渂latant attempt鈥 to reinforce insurgents in eastern Ukraine and de-stabilize the region, Stech said.

鈥淭hey are definitely losing their fight in eastern Ukraine,鈥 he said. 鈥淭he sanctions introduced by the west are starting to work and hurt their economy, and I think they are desperate.鈥

Diplomatic challenge 'extremely steep'

Dominique Arel, chair of Ukrainian studies at the University of Ottawa, called the convoy鈥檚 violation of Ukraine鈥檚 borders into cities like Luhansk an 鈥渆xtremely dangerous development鈥 that could lead to all-out urban warfare after weeks of intense shelling.

鈥淗ow do you actually defeat an urban insurgency? It鈥檚 one thing to take one village after the other 鈥. But urban warfare, it鈥檚 something else,鈥 Arel said on News Channel. 鈥淚鈥檓 not sure we鈥檙e really at the end game.鈥

Ahead of the summit, Arel said the diplomatic challenge is 鈥渆xtremely steep.鈥

鈥淩ussia refuses to acknowledge that it is actually sending military aid to the rebels, and refuses then to acknowledge that the border between Russia and Ukraine needs to be secured,鈥 he said.

A political settlement is ultimately necessary to bring security, Arel said.

鈥淎 claim of victory will not solve anything, especially if the border is not secure,鈥 Arel said. 鈥淏ut with whom, exactly, are you negotiating? Obviously, Ukraine and Russia needs to negotiate, but at ground level, with whom are you talking to if the actual de facto 鈥. leaders of this rebellion are actually Russian citizens鈥 that鈥檚 the big challenge.鈥