LONDON (Reuters) - Britain said on Monday it was supplying Ukraine with anti-tank weapons to help it defend itself from a potential invasion, during a stand-off with Russia which has massed troops near the Ukrainian border.

       Western countries say they fear Russia is preparing a pretext for a new assault on Ukraine, which it invaded in 2014.

       Moscow denies any plans for an attack, but has said it could take unspecified military action unless the West agrees to a list of demands, including banning Ukraine from ever joining NATO. Talks last week ended with no breakthrough. Kyiv has asked Western countries for arms to help it protect itself.

       "We have taken the decision to supply Ukraine with light anti-armour defensive weapon systems," British Defence Secretary Ben Wallace told parliament, saying the first systems were already delivered on Monday and a small number of British personnel would provide training for a short period of time.

       He did not specify the number or type of weapons that were being sent, but said: "They are not strategic weapons and pose no threat to Russia. They are to use in self-defence."

       "These are short-range .... but nevertheless it would make people pause and think what they were doing and if tanks were to roll into Ukraine, invade it, then they would be part of the defence mechanism."

       Wallace said he had invited Russian Defence Minister Sergei Shoigu to visit London in the next few weeks to discuss the crisis, though he did not know whether the Russians would accept.

       "The current gap is wide but not unbridgeable. I still remain hopefully that diplomacy will prevail. It is President (Vladimir) Putin’s choice," Wallace said.

       (Reporting by Kylie MacLellan and Alistair Smout; Editing by Kate Holton and Peter Graff)