A Russian foreign ministry official says Moscow fears that Britain could destroy key evidence in the nerve agent attack on an ex-Russian spy.

Former Russian double agent Sergei Skripal and his daughter remain in critical condition in the English city of Salisbury after being poisoned on March 4. Britain has blamed Russia for being behind the attack, and the case prompted the two nations to expel diplomats in a tit-for-tat dispute.

Vladimir Yermakov, deputy head of the ministry's department for non-proliferation, told a briefing for foreign envoys Wednesday that Britain is "hiding facts" and that key evidence might "disappear."

The Russian foreign ministry had invited foreign ambassadors in Moscow to brief them about the allegations, but the British and the U.S. missions shunned the meeting and sent lower-level diplomats instead.