There may not be any fighting in Ukraine yet but as tensions ratchet up in Crimea, young men in Kiev were queuing to sign up for the army, ready to take up arms if it comes to a war with Russia.

"I want to take part in the fight," said Roman Surzhikov, a 33-year-old engineer and army reservist, one of a steady stream of people going into an army recruitment centre in the city centre on Tuesday, despite a "closed" sign outside.

"Have they declared a general mobilisation yet?" he asked the woman at reception.

Ukraine's Black Sea peninsula of Crimea has been under the de facto control of pro-Kremlin forces in recent days, while President Vladimir Putin has reserved the right to send troops into the autonomous but mainly Russian-speaking region. He denies claims that Russian soldiers are already operating there.

"It's obvious an intervention is under way in Crimea and it's not impossible there will also be one on Ukrainian territory," Surzhikov told AFP as he explained why he wanted to enlist.

"I can't say I look forward to it, but if there is going to be a war, it's my duty. We have to defend the country," he said, adding that "10 million men are prepared to take up arms."

For now, he was told to just come back in a few days and leave his details. So far, only some Ukrainian army reservists are being called up and he was not one of them.

The Ukrainian army was put on alert over the weekend after Russia's parliament gave Putin permission to send troops into Ukraine, a former Soviet state.

In response, the head of Ukraine's national security and defence council Andriy Parubiy announced on Sunday that Kiev was to call up all military reservists, a move he said was to "ensure the security and territorial integrity of Ukraine".

While short of a general mobilisation, the announcement nevertheless drew hundreds of young men across the country eager to do their bit.

Television footage showed long queues in front of recruitment centres. The defence ministry declined to tell AFP how many had actually signed up, saying the information was top secret.

- 'Ready to defend our country' -

Faced with more volunteers than it could take, the recruitment office in central Kiev decided to shut its doors until Thursday.

Volodymyr Bykovski, who works at the office and has already been signed up himself, confirmed he had seen an influx of keen men -- young and old -- since the weekend.

"Most of them came on their own initiative" rather than being called up, he said, smoking a cigarette outside the centre, which was topped by the blue-and-yellow Ukrainian flag.

"Many are disappointed because they thought a mobilisation was already under way but we're still telling them to wait, that we'll call them when it's time."

Not just individuals but companies have stepped forward -- for example with computer equipment -- to help a Ukrainian army that has seen better days.

Compared to Russia's military force of some 845,000 troops, the armed forces here have six times fewer soldiers and their equipment is mostly outdated.

With this in mind, "people are scared of course, and I too am scared," said Bykovski. "But it has to be done, it's our duty."

This sense of patriotism in the face of stiff odds was shared by Dmytro Gerzhan, 42, who had just left his contact details with the recruitment office.

"If the situation gets more complicated -- who knows how things will develop, what Russia will do -- we have to join up," he said.

At another recruitment centre, Arthur said he was spurred to sign up by the memory of the nearly 100 protestors killed in the violence in Kiev's Independence Square which preceded the ousting of pro-Moscow president Viktor Yanukovych late last month.

"After what happened... it would be shameful not to go (and sign up)," the 23-year-old student said.

"I think it will all be resolved peacefully because the whole world is backing Ukraine and Ukraine has the truth on its side," he said.

"But if Putin decides to start a war against a brother nation, a lot of men will be ready to defend the country."