Brussels - EU leaders face a full agenda as they prepare to discuss Brexit, the nerve gas attack in Britain and proposed US tariffs during a two-day summit starting Thursday.

Leaders of the 27 countries that will remain in the European Union after Brexit were expected to approve guidelines for negotiating a future trade relationship with Britain, and to welcome the deal reached this week on a transitional period.

EU's response will be responsible

The leaders meeting in Brussels were also planning to respond to recent events including the nerve gas attack on former Russian spy Sergei Skripal and his daughter in the English city of Salisbury.

They were expected to show their solidarity with Britain, which has pointed the finger at Russia for the attack.

However, the bloc is not preparing any sanctions against Russia at this point, an EU official said ahead of the summit.

US tariffs on steel and aluminium products due to come into effect by the end of the week were also high on the leaders' agenda, as the EU seeks exemption from the levies.

"We must prepare for all possible scenarios," European Council President Donald Tusk said before the summit in a letter addressed to leaders.

"As the world's biggest trading power, the EU's response will be responsible and reasonable," he added.

The leaders were also planning to take stock of the EU's relations with Turkey, as the bloc's top officials prepare to meet Turkish President Recep Tayyip Erdogan in Varna, Bulgaria, on Monday for an EU-Turkey summit.