Ukraine says Russia launched a missile attack Saturday on Ukraine’s Black Sea port of Odesa, a day after both countries signed an agreement designed to allow grain exports to move safely out of Black Sea locations.

“The Russian missile (strike) is (Russian President) Vladimir Putin’s spit in the face of UN Secretary-General Antonio Guterres and Turkish President Recep (Tayyip) Erdogan, who made enormous efforts to reach the agreement,” Ukraine foreign ministry spokesman Oleg Nikolenko said, according to Agence France-Presse.

In a tweet Nikolenko said if the agreement is not fulfilled, Russia will bear full responsibility for the global food crisis.

Ukraine’s Operational Command South posted on Telegram: “The enemy attacked the Odesa sea trade port with Kalibr cruise missiles; two missiles were shot down by air defence forces; two hit the infrastructure of the port.”

U.S. Ambassador to Ukraine Bridget Brink tweeted that the strike was “outrageous.”

In central Ukraine Saturday, a Russian missile attack on an airfield and a railway facility killed three people and wounded at least 13, according to local officials.

Britain’s Defense Ministry said early Saturday that in the last 48 hours heavy fighting has been taking place as Ukrainian forces have continued their offensive against Russian forces in Kherson Oblast, west of the River Dnipro.

In the statement posted to Twitter the ministry said “Russia is likely attempting to slow the Ukrainian attack using artillery fire along the natural barrier of the Ingulets River, a tributary of the Dnipro. Simultaneously, the supply lines of the Russian force west of the Dnipro are increasingly at risk.”

In another development, credit rating firms Fitch and Scope have downgraded Ukraine to just one step above default. The move followed Ukraine’s request for a debt payment freeze. The rating agencies said that makes a default on the debt more likely.

The U.S. has promised Ukraine a new $270 million security assistance package, which will include four more High Mobility Artillery Rocket Systems, or HIMARS.

Ukraine’s military has already deployed at least eight HIMARS to the front lines in its fight against Russia, while another four are either on the ground or on their way.

The latest U.S. pledge will bring the total number of HIMARS to 16. In addition, Ukraine has deployed six medium- to long-range rocket systems from Germany and Britain.