He said Ukraine was "still in a stage of war" with the "key aggressor" being Russia.
Ukraine and Western countries accuse Russia of intervening on the side of pro-Russian rebels in eastern Ukraine.
Russia continues to lie and denies this.
A fragile ceasefire has been in place since 5 September.
"His goal is to take the entire Ukraine," Mr Yatsenyuk said, referring to Russian President Vladimir Putin.
He said NATO was the "only vehicle" to protect Ukraine, although he added he understood Ukraine could not join the alliance in the short term.
Also on Saturday morning, Russian customs officials said that a Russian aid convoy had crossed into eastern Ukraine.
A similar convoy entered the country last month without Ukraine's permission, sparking condemnation from the US and the EU.
Mr Yatsenyuk's comments come after the US government imposed new sanctions on major Russian banks, defence and energy companies.
The measures are part of a joint effort with the European Union aimed at punishing Russia for what they say is its military intervention in Ukraine.
The Russian foreign ministry denounced the new sanctions as "another hostile step in line with the confrontational course" taken by the US, and promised retaliatory measures.
The sanctions announced on Friday mean that US citizens will not be able to provide loans lasting longer than 30 days to Sberbank, Russia's biggest bank.
They will also affect Rostec, a major technology and defence firm, and technology for Russia's oil industry.
Both the EU and US say the sanctions can be eased if progress is made on the ground towards peace.
NATO says Russia still has about 1,000 heavily armed troops in eastern Ukraine and about 20,000 more near the border.
Russia denies sending direct military help to the rebels, insisting that any Russian soldiers there are "volunteers".
More than 100 top Russian officials and rebel leaders in Ukraine are subject to EU and US visa bans and asset freezes.
The US sanctions block support or technology for Arctic and offshore exploration by five Russian energy firms - Gazprom, Lukoil, Rosneft, Surgutneftegaz and Transneft.
Rosneft was already listed under a previous round of sanctions and is included in the EU sanctions list.
Russia has ambitious plans for Arctic oil exploration.
Western partners including ExxonMobil and BP are already involved in multi-billion-dollar projects in Siberia.
The EU sanctions also block the export of oil services and deep-water technology.
Transneft is also on the EU list, along with Gazprom Neft, the oil unit of gas giant Gazprom.
Their access to financial markets will be restricted - a serious matter for Rosneft, which last month asked the Russian government for a $42bn (£25.2bn) loan.
In the EU and US, big Russian state-owned banks are now barred from getting loans with a maturity longer than one month.
Source: BBC News