They said agreements on free trade and political association with the European Union were being stymied in particular by cases of "selective justice", a term used by the West to describe the prosecution of rival politicians, including former prime minister Tymoshenko, under President Viktor Yanukovich.
Ukraine hopes to sign the deals at a summit in Vilnius in November.
But Brussels has made it conditional on Kiev passing a number of legal reforms and addressing Western criticism of its justice and electoral systems.
"The stakes are very high and time is very short," Polish Foreign Minister Radoslaw Sikorski told reporters in Kiev on Thursday after meeting Yanukovich together with his colleagues from Lithuania, Denmark and the Netherlands.
"If the decision was to be taken now, I'm afraid, the answer on the signing would be 'no'," he said.
Yanukovich this month pardoned two former members of Tymoshenko's government who had been jailed on abuse-of-office charges, a move welcomed by Brussels.
But diplomats and analysts say he might be reluctant to do the same with regards to Tymoshenko, his fiercest political foe who led the 2004 Orange Revolution protests, derailing his first bid for presidency.
Tymoshenko was sentenced to seven years in prison in October 2011 on charges related to a 2009 gas deal with Russia which Yanukovich says has saddled Ukraine with an exorbitant energy prices.
Since last May, Tymoshenko, who has served twice as prime minister before narrowly losing the 2010 presidential run-off to Yanukovich, has been receiving treatment for back trouble in a state-run hospital in the city of Kharkiv.
Yanukovich himself says he cannot order her release because Tymoshenko is also due to be tried on tax evasion and embezzlement charges and is being investigated in a murder case.
She has denied all charges against her.
The EU shelved the deals with Ukraine over Tymoshenko in 2011, when they were initially due to be signed.
"You (Ukraine) have to dismiss all doubts about selective justice," Lithuanian Foreign Minister Linas Linkevicius told reporters when asked about Tymoshenko.
The EU says a deal needs to be sealed this year before the bloc turns its focus to European Parliament elections in 2014 and Ukraine itself holds a presidential election in 2015.
Poland's Sikorski urged Ukraine to act quickly.
"Ukraine has three critical months to do what is necessary... if we fail, we can spend decades, maybe generations arguing what went wrong," he said.
Source: Yahoo News