U.K. Prime Minister Theresa May announced a series of measures to punish Russia Wednesday, following a nerve agent attack on a former Russian spy and his daughter in Salisbury.

The measures include the expulsion of 23 Russian diplomats, the single biggest expulsion in over 30 years. May said the U.K. would also not send an official government representative to the soccer World Cup in Russia this year.

The U.K. “doesn’t want to break off all dialogue but this relationship cannot be the same,” May said in Parliament Wednesday, but announced that the U.K. is “suspending all high-level contact between the U.K. and Russia.”

Here is a list of the announcements:

  • U.K. to expel 23 Russian diplomats identified as “undeclared intelligence officers.” They have a week to leave, May said.
  • U.K. to “degrade Russian intelligence capability for years to come” and will take immediate action to “dismantle espionage network.”
  • U.K. to “harden defenses against hostile state activity in the U.K.”
  • Strengthened sanctions against the abuse of human rights.
  • U.K. government to use powers to monitor and track those coming to the U.K. who could threaten the country.
  • Foreign Minister Sergei Lavrov’s invitation to the U.K. is revoked.

We have disagreements with the people of Russia, May said, and “it is tragic that President (Vladimir) Putin has chosen to act in this way.”

She added that the U.K. does not stand alone in “confronting Russian aggression,” saying that she had spoken with the leaders of the U.S., France and Germany.

The penalties mark the most serious deterioration in U.K.- Russia relations in recent years.

They come after Sergei Skripal, a former Russian spy turned double agent for the U.K., and his daughter Yulia, were subject to a nerve agent attack in early March for which they remain in a critical condition in hospital.

Earlier this week, May said it was “highly likely” that Russia was behind the attack that saw a Russian-developed nerve agent, part of the “Novichok” series of deadly chemical weapons, used against the pair.

Earlier on Wednesday, ahead of the penalties, Russian Foreign Minister Sergei Lavrov rubbished the U.K.’s allegations, saying the country was “misleading the international community.”