The European Union (EU) has agreed on new sanctions against Russia but is waiting a "few days" before implementing them, EU President Herman Van Rompuy said on Monday.
"The [sanctions'] entry into force (..) will take place in the next few days," Van Rompuy said.
He indicated that "this will leave time for an assessment of the implementation of the [Ukraine] ceasefire agreement and the peace plan."
"Depending on the situation on the ground, the EU stands ready to review the agreed sanctions in whole or in part," he added.
Despite a ceasefire agreemed between Ukraine and pro Russia forces on Setpember 5, clashes continue.. Both sides have accused each other of breaching the ceasefire agreement.
However, the Ukrainian presidency said "the two sides continued to coordinate actions in support of the ceasefire".
The Kremlin added that the two leaders -- speaking by phone often despite only having met twice since Poroshenko's election in May -- agreed to continue discussing "steps to facilitate a peaceful resolution of the situation in southeast Ukraine", the AFP news agency reports.
Poroshenko used his solidarity visit to the southeastern port of Mariupol -- the only major conflict zone city still under government control -- to boost both morale and hopes that Ukraine's worst crisis since its 1991 independence was drawing to a close.
"It is our land. We will not give it up to anyone," Poroshenko tweeted on his arrival.
Mariupol has been on edge fearing a full-on offensive by rebels who have advanced across the southeast in late August apparently backed by Russian troops and firepower, and dramatically reversed recent Ukrainian gains.
"It is impossible to win the conflict just by military means," he told reporters.
"The more we increase the pressure, the more Russian troops are on our territory," he said in his most substantive comments since the Minsk "protocol" was signed.
'Truce alone not enough'
He said there had been 10-12 violations of the ceasefire and called on the OSCE, the pan-European security body that brokered the deal, to send observers to the "dangerous" spots where violence had flared.
European leaders have been keen to ensure a halt to the fighting that has rattled financial markets and provoked a trade war with Russia, damaging farmers and threatening the economic recoveries of leading EU nations such as Germany.
"The ceasefire in itself alone is not enough," Swiss president and OSCE head Didier Burkhalter said.
"We need a political process, national dialogue (and) dialogue between the two presidents."
Poroshenko also sparked brief confusion by announcing that "we have managed to free 1,200 of our prisoners" since the ceasefire deal.
A source close to the president later told AFP that Poroshenko meant to say that the rebels had seized around that number of Ukrainians during the conflict.
The official said insurgents had released 648 captives since the fighting broke out across the industrial east in mid-April and more than 500 others are expected to be released.
Ukraine's defence spokesman had earlier said the rebels had handed over 20 government soldiers since Friday as part of the prisoner swap agreed under the 12-point peace pact.
'Ready to review sanctions'
The two presidents' promise to work jointly on ending the worst East-West crisis since the Cold War came shortly before the European Union agreed new sanctions against Russia's energy and defence sectors.
But the measures will not come into force until they are published in the EU's official journal, which can take several days, and the sanctions could still be suspended if the ceasefire holds.
"Depending on the situation on the ground, the EU stands ready to review the agreed sanctions in whole or in part," European Council President Herman Van Rompuy said.
Russian Prime Minister Dmitry Medvedev had already warned that new punitive steps would see Moscow adopt "asymmetrical" measure that could see EU airlines banned from flying over the country's airspace on their lucrative Asian routes.
Diplomats said new restrictions bar Russia's largest state-owned oil and defence firms from using European markets to raise capital for everyday operations and vital investments.
The bans are a particularly big blow to Rosneft -- the Russian oil giant that is run by a close Putin ally and has gone tens of billions of dollars in debt while making acquisitions that have made it the world's largest publicly trade producer of crude.
The bans also apply to the oil division of natural gas giant Rosneft and the oil pipeline monopoly Transneft.
The 28-nation EU bloc also agreed to slap more asset freezes and travel bans on officials either implicated in the Ukraine crisis or viewed as playing an important role in forming Putin's policies.